1 00:00:02,000 --> 00:00:03,250 WILLIAM SHATNER: Massive caverns 2 00:00:03,375 --> 00:00:06,417 that stretch for miles into the darkness. 3 00:00:06,542 --> 00:00:12,083 Underwater caves believed to be portals to the underworld. 4 00:00:12,208 --> 00:00:15,875 And an ancient subterranean wonder 5 00:00:16,042 --> 00:00:19,958 that may hide the remains of a monster. 6 00:00:21,417 --> 00:00:25,292 Just below Earth's vast and diverse landscape 7 00:00:25,458 --> 00:00:29,000 lies thousands of tunnels and caves. 8 00:00:29,125 --> 00:00:32,542 While some have been carved by the forces of nature 9 00:00:32,708 --> 00:00:34,542 over millions of years, 10 00:00:34,708 --> 00:00:38,708 others were painstakingly created by human hands. 11 00:00:38,875 --> 00:00:42,083 Since the dawn of mankind, underground passageways 12 00:00:42,250 --> 00:00:45,417 have been used as a place to perform secret rituals 13 00:00:45,583 --> 00:00:49,333 preserve human remains and, according to some, 14 00:00:49,542 --> 00:00:55,292 serve as gateways to the realm of the supernatural. 15 00:00:56,375 --> 00:00:59,958 What mysteries of the underworld are hiding 16 00:01:00,125 --> 00:01:02,875 in the dark recesses below us? 17 00:01:03,000 --> 00:01:07,458 Well, that is what we'll try and find out. 18 00:01:07,583 --> 00:01:09,542 ♪ ♪ 19 00:01:22,208 --> 00:01:24,333 SHATNER: It's sometimes hard to believe that on a planet 20 00:01:24,417 --> 00:01:26,542 populated by eight billion people, 21 00:01:26,708 --> 00:01:31,167 there could still be places in this world yet to be explored. 22 00:01:31,333 --> 00:01:35,667 But such is the case with the majority of caverns and caves 23 00:01:35,833 --> 00:01:41,000 that ramble and weave deep inside Earth's surface. 24 00:01:42,042 --> 00:01:44,458 JILL HEINERTH: Very few caves on the planet have been explored 25 00:01:44,583 --> 00:01:47,292 because they're difficult to get to. 26 00:01:47,500 --> 00:01:50,750 There'll be caves deeper than any human has ever been before, 27 00:01:50,875 --> 00:01:55,667 and in remote places and mountaintops we can't yet reach. 28 00:01:55,875 --> 00:02:00,292 It's, um, also taboo in some cultures even to go into caves. 29 00:02:01,375 --> 00:02:04,083 I've been cave diving all around the world 30 00:02:04,250 --> 00:02:07,500 and when I get to explore a cave, 31 00:02:07,667 --> 00:02:12,167 I'm often the first and only person to ever go inside there. 32 00:02:12,333 --> 00:02:14,708 Probably 90% of the caves on this planet 33 00:02:14,917 --> 00:02:17,125 haven't even been explored yet 34 00:02:17,208 --> 00:02:20,583 and yet, we're finding so many unique things. 35 00:02:21,750 --> 00:02:24,125 Caves have so much to teach us, 36 00:02:24,292 --> 00:02:28,042 both dry caves and underwater caves. 37 00:02:28,208 --> 00:02:31,250 Even the species that we recognize inside caves 38 00:02:31,417 --> 00:02:33,125 behave differently. 39 00:02:34,167 --> 00:02:37,125 I mean, we're talking about a completely dark, 40 00:02:37,292 --> 00:02:39,208 food-scarce environment, 41 00:02:39,375 --> 00:02:42,667 and yet, there are animals that are living within these caves 42 00:02:42,792 --> 00:02:47,000 that have not evolved in more than 65 million years. 43 00:02:47,167 --> 00:02:48,875 We've already sequenced 44 00:02:49,042 --> 00:02:54,625 more than 4,000 different types of bacteria growing in caves. 45 00:02:54,833 --> 00:03:00,667 And these are sources for future chemicals, for future medicines. 46 00:03:00,792 --> 00:03:02,708 We also have astrobiologists 47 00:03:02,875 --> 00:03:05,625 that are interested in the microbes that live 48 00:03:05,792 --> 00:03:09,292 in these really harsh environments of caves 49 00:03:09,500 --> 00:03:13,708 and, um, this could be the clue to life on other planets. 50 00:03:14,750 --> 00:03:18,000 SHATNER: While caves offer boundless potential 51 00:03:18,208 --> 00:03:21,042 to unlock the natural secrets of our planet-- 52 00:03:21,250 --> 00:03:24,333 and even worlds beyond our own-- 53 00:03:24,500 --> 00:03:28,792 they also hide the story of mankind's ancient past. 54 00:03:29,875 --> 00:03:33,208 For instance, Wonderwerk Cave in South Africa 55 00:03:33,375 --> 00:03:35,125 has archeological evidence 56 00:03:35,292 --> 00:03:39,292 that our ancestors lived in caves for two million years. 57 00:03:40,208 --> 00:03:42,167 But just as it was for ancient man, 58 00:03:42,292 --> 00:03:45,167 Earth's mysterious underground 59 00:03:45,333 --> 00:03:47,708 is still one of the most dangerous 60 00:03:47,875 --> 00:03:50,792 environments imaginable. 61 00:03:50,875 --> 00:03:53,875 There are a lot of hazards involved in exploring caves 62 00:03:54,042 --> 00:03:56,750 because, uh, uh, you're going into an environment 63 00:03:56,875 --> 00:03:58,458 that's completely dark... 64 00:03:59,542 --> 00:04:01,292 ...and you have to have the right equipment. 65 00:04:01,458 --> 00:04:04,708 If your batteries run out, then you're screwed. 66 00:04:04,875 --> 00:04:06,333 If you're far back in a cave 67 00:04:06,500 --> 00:04:08,750 and you don't have a light to get out. 68 00:04:08,958 --> 00:04:11,625 A lot of caves involve a significant vertical component 69 00:04:11,792 --> 00:04:13,083 to the exploration 70 00:04:13,250 --> 00:04:14,958 where you have to rappel down into them, 71 00:04:15,125 --> 00:04:18,500 and you have to use ascenders to get out, rope ascenders. 72 00:04:18,667 --> 00:04:22,375 I was on this one expedition into a cave in New Mexico 73 00:04:22,542 --> 00:04:26,250 where, uh, one of the people on my... on-on my team 74 00:04:26,417 --> 00:04:28,583 got stuck and couldn't get out. 75 00:04:28,750 --> 00:04:31,167 And so, we had to send a team to the surface 76 00:04:31,333 --> 00:04:33,458 to get tools to bring back down in there 77 00:04:33,625 --> 00:04:35,125 to chop away at the rock to get him out. 78 00:04:35,250 --> 00:04:36,458 Because we knew it would be several hours 79 00:04:36,625 --> 00:04:38,000 before a rescue team could get there. 80 00:04:39,625 --> 00:04:43,500 If it's a submerged cave, the danger is even greater. 81 00:04:43,625 --> 00:04:45,000 It's not uncommon for the floor of the cave 82 00:04:45,208 --> 00:04:46,750 to be covered with silt. 83 00:04:46,917 --> 00:04:50,333 And if you get too close to it and your flipper hits it, 84 00:04:50,458 --> 00:04:53,292 it'll silt up, you'll get a complete whiteout. 85 00:04:53,417 --> 00:04:54,667 You won't be able to see, 86 00:04:54,875 --> 00:04:57,333 your visibility suddenly goes to zero. 87 00:04:57,458 --> 00:04:59,708 I've heard stories about cave divers who drowned 88 00:04:59,875 --> 00:05:02,833 and they were only about 50 feet from the entrance to the cave 89 00:05:03,042 --> 00:05:07,250 because they-th-th-they had no visibility at all. 90 00:05:08,625 --> 00:05:10,542 SHATNER: Exploring Earth's underground 91 00:05:10,708 --> 00:05:13,583 sounds like a potentially deadly proposition. 92 00:05:13,750 --> 00:05:18,125 But despite the inherent risks, every so often 93 00:05:18,250 --> 00:05:20,667 a new cave system is discovered 94 00:05:20,833 --> 00:05:26,292 that takes your breath away from its sheer beauty and wonder. 95 00:05:35,667 --> 00:05:38,167 SHATNER: Local lumberjack, Ho Khanh, 96 00:05:38,333 --> 00:05:40,833 searches the dense jungle for agarwood-- 97 00:05:41,042 --> 00:05:44,958 a valuable fragrant wood found in Aquilaria trees-- 98 00:05:45,083 --> 00:05:49,583 when he stumbles upon something monumental. 99 00:05:51,167 --> 00:05:54,292 (translated): I went into the forest to search for agarwood. 100 00:05:54,500 --> 00:05:56,833 One afternoon, when it started to rain, 101 00:05:56,958 --> 00:05:58,833 I sought shelter. 102 00:06:00,625 --> 00:06:04,083 I found a mysterious cave entrance, 103 00:06:04,250 --> 00:06:06,917 which was unlike any other caves in the area. 104 00:06:09,792 --> 00:06:13,667 The entrance was covered with a thick layer of mist and steam, 105 00:06:13,833 --> 00:06:16,083 and there was wind blowing out from it. 106 00:06:19,792 --> 00:06:24,167 I'm the very person who discovered Son Doong Cave, 107 00:06:24,250 --> 00:06:26,125 the world's largest cave. 108 00:06:27,167 --> 00:06:29,958 SHATNER: Ho Khanh's remarkable discovery was so difficult to find, 109 00:06:30,083 --> 00:06:33,708 it took him 18 years to properly retrace his steps 110 00:06:33,875 --> 00:06:37,500 and locate the caves hidden entrance once again. 111 00:06:38,917 --> 00:06:40,708 And in 2009, 112 00:06:40,833 --> 00:06:44,292 he successfully shared the remote underground world 113 00:06:44,458 --> 00:06:48,333 with British cave explorer Howard Limbert. 114 00:06:49,292 --> 00:06:52,542 To get to Son Doong Cave it's-it's quite an expedition. 115 00:06:52,708 --> 00:06:54,417 It's not next to the road. 116 00:06:54,583 --> 00:06:57,167 It takes a day and a half walk. 117 00:06:57,333 --> 00:06:59,417 And the only way to get to Son Doong 118 00:06:59,583 --> 00:07:02,375 is to come through Swallow Cave. 119 00:07:02,542 --> 00:07:05,292 And it's where we sleep the first night. 120 00:07:05,458 --> 00:07:08,708 And the next day we go through this cave, 121 00:07:08,875 --> 00:07:12,500 through a hidden valley to get to Son Doong. 122 00:07:12,667 --> 00:07:15,375 That's the only way into Son Doong. 123 00:07:15,583 --> 00:07:18,917 So, it's quite an adventure to get just to the entrance. 124 00:07:19,042 --> 00:07:22,625 But the number of people that have been in Son Doong 125 00:07:22,708 --> 00:07:24,667 is less than the number of people 126 00:07:24,875 --> 00:07:27,625 that have climbed Mount Everest. 127 00:07:27,750 --> 00:07:31,500 We're very strict on conservation within the cave. 128 00:07:31,708 --> 00:07:34,500 We restrict the number of people that come into Son Doong 129 00:07:34,625 --> 00:07:36,750 to protect the cave. 130 00:07:37,792 --> 00:07:41,000 Thus not many people have a chance to visit Son Doong. 131 00:07:41,208 --> 00:07:44,208 It certainly is one of the Great Wonders of the World, 132 00:07:44,375 --> 00:07:48,792 and it should retain its beauty for all the generations ahead. 133 00:07:49,792 --> 00:07:51,708 BEN McGEE: So visualize this 134 00:07:51,875 --> 00:07:54,875 journey to the center of the Earth kind of place 135 00:07:55,042 --> 00:07:56,792 with its own forest, and its own sunlight, 136 00:07:56,875 --> 00:07:58,333 its own ecosystem, its own river. 137 00:07:58,542 --> 00:07:59,708 And it is so big, 138 00:07:59,875 --> 00:08:03,458 you can fit 76 Mount Rushmore's inside 139 00:08:03,625 --> 00:08:05,708 or 15 Pyramids of Giza. 140 00:08:05,875 --> 00:08:10,083 This really is more than a city underground. 141 00:08:11,208 --> 00:08:15,083 LIMBERT: We found seven new species in the last few years in Son Doong. 142 00:08:15,292 --> 00:08:18,833 Such as white fish, a cave spider, 143 00:08:19,042 --> 00:08:23,375 and other small creatures we found in the cave. 144 00:08:23,500 --> 00:08:26,667 Also, it's got some incredibly rare plants. 145 00:08:26,833 --> 00:08:30,333 There's one plant that's only seen as a pressing in a museum. 146 00:08:30,542 --> 00:08:32,583 So, there's lots and lots of rare things 147 00:08:32,750 --> 00:08:34,750 within Son Doong that we've found. 148 00:08:35,708 --> 00:08:37,583 And, in fact, there's still new passages 149 00:08:37,750 --> 00:08:39,667 to be found in Son Doong. 150 00:08:40,667 --> 00:08:43,667 We've dived the very end of Son Doong 151 00:08:43,792 --> 00:08:45,875 and it's still continuing. 152 00:08:46,042 --> 00:08:49,667 But we need special gases so we can dive deeper. 153 00:08:49,833 --> 00:08:52,792 But there's a good chance we can join Son Doong 154 00:08:52,917 --> 00:08:55,875 with another cave, which will make it even bigger. 155 00:08:57,042 --> 00:09:00,500 The beauty about exploring caves like Son Doong 156 00:09:00,625 --> 00:09:04,208 is you don't know what you're going to find. 157 00:09:04,375 --> 00:09:08,042 So, we don't know what the next discovery's going to be. 158 00:09:15,958 --> 00:09:17,792 SHATNER: Beneath the rolling hills, 159 00:09:17,958 --> 00:09:20,167 deep river valleys and dense forest 160 00:09:20,333 --> 00:09:22,792 lies one of the most awe-inspiring 161 00:09:22,917 --> 00:09:25,875 underground environments on planet Earth. 162 00:09:26,875 --> 00:09:28,833 It's a UNESCO World Heritage Site 163 00:09:29,000 --> 00:09:32,667 visited by 600,000 people every year 164 00:09:32,833 --> 00:09:36,500 called Mammoth Cave National Park. 165 00:09:37,542 --> 00:09:40,500 SCHROER: Mammoth Cave is the longest cave system in the world 166 00:09:40,667 --> 00:09:43,875 at around 426 miles. 167 00:09:44,042 --> 00:09:46,417 Now, that is what we know of today. 168 00:09:46,583 --> 00:09:48,250 We are still mapping Mammoth Cave. 169 00:09:48,375 --> 00:09:52,458 There's still more cave to be found, more passages to explore. 170 00:09:52,625 --> 00:09:54,333 So every year, we just add on to that mileage, 171 00:09:54,500 --> 00:09:55,333 and at this point, 172 00:09:55,542 --> 00:09:56,833 there's no end in sight. 173 00:09:56,958 --> 00:09:59,000 It leaves a lot to your imagination 174 00:09:59,208 --> 00:10:02,208 to look out into the darkness and wonder 175 00:10:02,375 --> 00:10:04,875 what could be out there. 176 00:10:05,000 --> 00:10:08,458 I've been in Mammoth Cave easily more than 500 times. 177 00:10:08,625 --> 00:10:11,000 It's a very complex cave system. 178 00:10:11,208 --> 00:10:14,667 And it's got, very, very old levels that are dry, 179 00:10:14,833 --> 00:10:17,583 and then the most recent levels have active rivers 180 00:10:17,708 --> 00:10:19,542 flowing in them. 181 00:10:19,667 --> 00:10:22,958 Mammoth Cave looks like a big maze. 182 00:10:23,125 --> 00:10:25,125 And there are numerous cave systems 183 00:10:25,250 --> 00:10:28,167 that could potentially connect and make it longer. 184 00:10:28,375 --> 00:10:30,917 So, we think that Mammoth Cave 185 00:10:31,083 --> 00:10:33,958 has the potential to be a thousand miles long. 186 00:10:34,125 --> 00:10:37,333 And so, I'm anticipating that I will find more cave. 187 00:10:37,542 --> 00:10:40,833 SHATNER: While scientists continue to map and explore 188 00:10:41,000 --> 00:10:43,417 the uncharted depths of Mammoth Cave, 189 00:10:43,625 --> 00:10:45,792 there is a different kind of darkness 190 00:10:45,917 --> 00:10:48,750 that dwells in Kentucky's famed underground... 191 00:10:50,000 --> 00:10:53,542 ...a dread that hovers over this cavern's history 192 00:10:53,708 --> 00:10:56,333 of tragic deaths. 193 00:10:56,458 --> 00:10:58,000 The most well-known tragedy involved 194 00:10:58,208 --> 00:11:01,167 a legendary cave explorer from the early 1900s 195 00:11:01,375 --> 00:11:04,167 named Floyd Collins. 196 00:11:05,542 --> 00:11:06,875 SCHROER: Floyd Collins was not afraid 197 00:11:07,083 --> 00:11:08,917 to go through the really tight passages, 198 00:11:09,083 --> 00:11:11,333 or to go where nobody had ever been before. 199 00:11:12,375 --> 00:11:14,667 One of the big discoveries Floyd had in his time 200 00:11:14,875 --> 00:11:17,750 was a cave called Crystal Cave. 201 00:11:17,917 --> 00:11:20,833 And it is one of the most beautiful caves that we have 202 00:11:21,000 --> 00:11:23,583 in Mammoth Cave National Park right now. 203 00:11:23,792 --> 00:11:29,583 In 1925, he entered into a cave known as Sand Cave. 204 00:11:29,750 --> 00:11:33,792 Unfortunately, Floyd went in in late January, 205 00:11:33,958 --> 00:11:36,292 and he did not come back out. 206 00:11:37,333 --> 00:11:40,542 No one knew where Floyd was until they went exploring 207 00:11:40,708 --> 00:11:43,167 outside of Sand Cave and they saw Floyd's jacket. 208 00:11:44,208 --> 00:11:46,667 His brother yelled down, "Floyd, are you down there?" 209 00:11:46,792 --> 00:11:50,083 And Floyd yelled out, "Help me. Get me out of here." 210 00:11:50,250 --> 00:11:53,792 It was a big national news story of the day. 211 00:11:53,958 --> 00:11:55,792 He was just stuck. 212 00:11:56,000 --> 00:11:58,083 He was unable to move his arms. He couldn't reach his feet. 213 00:11:58,208 --> 00:12:01,167 They described it as a limestone straightjacket. 214 00:12:01,333 --> 00:12:02,667 It's just a terrifying thing 215 00:12:02,833 --> 00:12:04,333 to think of being stuck inside the cave. 216 00:12:04,542 --> 00:12:08,083 And they gave as much effort as they could to get him out. 217 00:12:09,333 --> 00:12:12,750 After two weeks of a statewide, national 218 00:12:12,917 --> 00:12:15,833 and local effort to try to get Floyd out, 219 00:12:16,000 --> 00:12:18,917 he unfortunately died inside the cave. 220 00:12:21,375 --> 00:12:25,500 KAMBESIS: Mammoth Cave does have a reputation of being haunted. 221 00:12:25,625 --> 00:12:28,958 There's lots of stories about people 222 00:12:29,167 --> 00:12:32,083 having experiences in the cave that they can't really explain. 223 00:12:33,042 --> 00:12:35,000 I mean, I've had an experience where 224 00:12:35,208 --> 00:12:37,667 I thought I felt, like, a presence there. 225 00:12:37,875 --> 00:12:40,083 That's a little bit unsettling. (laughing) 226 00:12:40,208 --> 00:12:42,750 Lots of people, they're convinced 227 00:12:42,917 --> 00:12:46,167 that it's Floyd Collins' ghost that's haunting that cave. 228 00:12:46,375 --> 00:12:49,167 I mean, his coffin was in Crystal Cave for decades 229 00:12:49,333 --> 00:12:52,958 before they had a proper burial and put him on the surface. 230 00:12:55,208 --> 00:12:58,833 SHATNER: Is Mammoth Cave really haunted by the spirit of Floyd Collins? 231 00:13:00,000 --> 00:13:01,917 While many certainly believe it's true, 232 00:13:02,083 --> 00:13:04,500 there are other tragic deaths that occurred 233 00:13:04,667 --> 00:13:07,208 in Kentucky's subterranean world 234 00:13:07,375 --> 00:13:13,333 that may also be the source of lingering, restless spirits. 235 00:13:14,333 --> 00:13:15,667 There was a doctor named John Croghan 236 00:13:15,833 --> 00:13:18,333 who purchased Mammoth Cave in 1839 237 00:13:18,458 --> 00:13:21,708 and there was this thought that maybe the different air 238 00:13:21,917 --> 00:13:25,792 in the cave could actually cure tuberculosis. 239 00:13:25,958 --> 00:13:29,917 And so, he had an entire facility 240 00:13:30,042 --> 00:13:31,958 built inside Mammoth Cave, 241 00:13:32,083 --> 00:13:34,500 where they would take critically-ill 242 00:13:34,708 --> 00:13:37,417 tuberculosis patients, with the hopes 243 00:13:37,583 --> 00:13:39,375 that they would get better. 244 00:13:39,542 --> 00:13:40,792 And of course, they didn't. 245 00:13:40,958 --> 00:13:43,042 After a few years, everyone died. 246 00:13:44,042 --> 00:13:45,833 SHATNER: While their deaths certainly add another layer 247 00:13:46,042 --> 00:13:49,042 to Mammoth Cave's haunted reputation, 248 00:13:49,208 --> 00:13:52,833 it's possible that spirits have inhabited this cave 249 00:13:53,042 --> 00:13:54,875 for thousands of years. 250 00:13:56,042 --> 00:13:57,958 Because in the early 1800s, 251 00:13:58,125 --> 00:14:02,000 miners were surprised to discover that the cave 252 00:14:02,167 --> 00:14:06,250 was once an ancient burial ground. 253 00:14:07,250 --> 00:14:11,167 People began finding evidence not just of prior mining 254 00:14:11,375 --> 00:14:13,458 but of prior ritual use. 255 00:14:14,500 --> 00:14:19,375 One of the finds was what is clearly a crypt. 256 00:14:19,542 --> 00:14:23,833 Inside was the mummy of a Native American woman. 257 00:14:24,875 --> 00:14:27,875 She was preserved almost perfectly. 258 00:14:28,042 --> 00:14:32,042 According to accounts, she was draped in deer skins 259 00:14:32,208 --> 00:14:36,750 that were decorated with leaves and vines and things like this. 260 00:14:36,917 --> 00:14:41,125 This is really clearly a thoughtful ritual burial. 261 00:14:41,292 --> 00:14:43,333 She did get the name Fawn Hoof, because she had a necklace 262 00:14:43,500 --> 00:14:45,875 of-of hooves from fawns. 263 00:14:46,042 --> 00:14:49,125 And she apparently was buried with a lot of items 264 00:14:49,250 --> 00:14:51,917 and plants that you might expect of someone 265 00:14:52,083 --> 00:14:54,333 who was a healer to carry with them. 266 00:14:54,458 --> 00:14:56,917 She would have been a person of high status in the society, 267 00:14:57,042 --> 00:14:58,833 someone looked up to. 268 00:14:59,042 --> 00:15:00,958 She was buried with things that they may have thought 269 00:15:01,125 --> 00:15:03,000 she needed for an afterlife. 270 00:15:04,500 --> 00:15:07,000 SHATNER: It was reported that several other Native American mummies 271 00:15:07,208 --> 00:15:08,917 were dug out of Mammoth Cave, 272 00:15:09,083 --> 00:15:13,167 including one found in 1935 nicknamed "Lost John," 273 00:15:13,333 --> 00:15:16,417 who would eventually be displayed inside the cave 274 00:15:16,542 --> 00:15:18,292 as a tourist attraction. 275 00:15:18,375 --> 00:15:21,083 Many have wondered, could the desecration 276 00:15:21,250 --> 00:15:24,708 of this ancient burial ground and its mummified human remains 277 00:15:24,917 --> 00:15:29,375 explain the otherworldly presence reported here? 278 00:15:30,875 --> 00:15:34,042 The scientists estimate that some of the remains 279 00:15:34,167 --> 00:15:37,333 that were found in the cave date back 5,000 years. 280 00:15:37,542 --> 00:15:40,917 Babies have been found in there, one which was brought out 281 00:15:41,042 --> 00:15:44,583 and, within a few hours, completely disintegrated. 282 00:15:45,750 --> 00:15:47,708 You have to understand that the caves 283 00:15:47,875 --> 00:15:49,417 would have been considered sacred 284 00:15:49,542 --> 00:15:52,333 by these different tribes in the area. 285 00:15:52,500 --> 00:15:55,000 In many Native American cultures, 286 00:15:55,208 --> 00:15:58,667 caves are the entrance to the underworld. 287 00:15:58,875 --> 00:16:01,292 These are places where you go 288 00:16:01,458 --> 00:16:04,333 to commune with the spirits of the dead. 289 00:16:05,583 --> 00:16:09,375 There's catastrophic loss of human life in there, 290 00:16:09,542 --> 00:16:13,167 and a lot of mysticism that goes along with it. 291 00:16:13,333 --> 00:16:17,542 And at the time, these mummies became attractions 292 00:16:17,708 --> 00:16:20,333 for tourists to come look. 293 00:16:21,875 --> 00:16:23,292 KAMBESIS: Every once in a while, 294 00:16:23,500 --> 00:16:26,000 you get a sense that there's a presence there. 295 00:16:27,250 --> 00:16:29,250 You'll start to hear things, 296 00:16:29,417 --> 00:16:32,042 like there's something there besides you. 297 00:16:32,917 --> 00:16:35,375 And sometimes, it's scary. 298 00:16:35,542 --> 00:16:37,167 But many cave explorers that I know 299 00:16:37,333 --> 00:16:39,000 have explained the same thing. 300 00:16:39,208 --> 00:16:43,208 That there's an unexplained phenomenon in this cave. 301 00:16:44,833 --> 00:16:46,792 So, what do you think? 302 00:16:47,000 --> 00:16:50,000 Could the discovery of mummies at Mammoth Cave 303 00:16:50,167 --> 00:16:53,167 have riled the spirits of those laid to rest there? 304 00:16:53,333 --> 00:16:58,042 Perhaps some places are best left undisturbed. 305 00:16:58,167 --> 00:17:01,958 Like in the case of an underwater cave system 306 00:17:02,083 --> 00:17:05,667 in Mexico that may be guarded 307 00:17:05,833 --> 00:17:08,375 by a powerful serpent. 308 00:17:18,458 --> 00:17:20,375 SHATNER: A six-mile-wide space rock 309 00:17:20,542 --> 00:17:22,250 smashes into Earth... 310 00:17:24,125 --> 00:17:26,167 ...and sends billions of tons of rock and debris 311 00:17:26,375 --> 00:17:29,583 into the atmosphere, generating tsunamis 312 00:17:29,750 --> 00:17:31,417 that are half a mile high. 313 00:17:32,333 --> 00:17:34,667 This apocalyptic impact 314 00:17:34,875 --> 00:17:39,208 kills 75% of all life on the planet, 315 00:17:39,375 --> 00:17:43,083 and creates about 6,000 sinkholes 316 00:17:43,208 --> 00:17:49,083 and underwater cave systems known as cenotes. 317 00:17:49,833 --> 00:17:53,125 Cenotes are one of the principal sources of water in the Yucatán. 318 00:17:53,333 --> 00:17:56,000 So, all of the movement of water 319 00:17:56,167 --> 00:17:57,708 in the Yucatán, practically all the movement 320 00:17:57,875 --> 00:18:00,042 of water in the Yucatán occurs in the subsurface. 321 00:18:01,417 --> 00:18:05,000 A cenote is literally a hole in the ground, 322 00:18:05,208 --> 00:18:07,792 and it's usually flooded at the bottom. 323 00:18:07,958 --> 00:18:10,792 The ancient Mayans used the cenotes 324 00:18:11,000 --> 00:18:13,333 on the Yucatán Peninsula for a water supply. 325 00:18:13,542 --> 00:18:17,458 And the cenotes also have cultural significance 326 00:18:17,625 --> 00:18:21,458 because of the role that they played in Mayan religion 327 00:18:21,625 --> 00:18:24,208 and Mayan agriculture. 328 00:18:26,042 --> 00:18:29,208 SHATNER: Cenotes were sacred to the ancient Mayan civilization 329 00:18:29,375 --> 00:18:33,000 who existed in the region for about 3,500 years 330 00:18:33,167 --> 00:18:35,458 starting around 2000 BC. 331 00:18:36,542 --> 00:18:39,250 These natural wells of freshwater 332 00:18:39,375 --> 00:18:43,375 were essential for growing crops and clean drinking water. 333 00:18:43,542 --> 00:18:46,958 In fact, one of the Mayan's most important cities 334 00:18:47,167 --> 00:18:50,250 on the Yucatán Peninsula was called Mayapan, 335 00:18:50,375 --> 00:18:52,833 and it was purposefully constructed 336 00:18:53,042 --> 00:18:56,125 around these vital water sources. 337 00:18:56,292 --> 00:18:57,833 LYNNE McNEILL: Mayapan was a really 338 00:18:58,042 --> 00:19:00,000 sprawling, beautiful city 339 00:19:00,208 --> 00:19:03,333 built entirely inside a protective wall. 340 00:19:03,500 --> 00:19:07,167 And within that wall that surrounds it, 341 00:19:07,333 --> 00:19:10,500 there are a number of cenotes. 342 00:19:10,625 --> 00:19:13,250 Which, of course, if you're an ancient civilization 343 00:19:13,458 --> 00:19:15,167 looking for a fresh water supply, 344 00:19:15,375 --> 00:19:18,333 this would have been a phenomenal place 345 00:19:18,542 --> 00:19:21,667 to build your walled city and make sure that you contain 346 00:19:21,875 --> 00:19:23,583 all of those bodies of water. 347 00:19:23,708 --> 00:19:28,292 But what's really interesting is that there is one cenote 348 00:19:28,458 --> 00:19:30,333 that is outside the city walls. 349 00:19:30,458 --> 00:19:35,667 And this particular cenote is known as Sac Uayum. 350 00:19:35,875 --> 00:19:39,750 And it's not incidentally outside the city walls. 351 00:19:39,958 --> 00:19:42,125 The city walls actually zigzag 352 00:19:42,292 --> 00:19:43,958 in this really awkward way 353 00:19:44,125 --> 00:19:47,958 around this one pool of water. 354 00:19:48,125 --> 00:19:50,458 SHATNER: Why would the ancient Mayans 355 00:19:50,625 --> 00:19:53,083 go through all the effort to build around 356 00:19:53,250 --> 00:19:57,208 this one cenote known as Sac Uayum? 357 00:19:57,417 --> 00:20:01,375 Perhaps answers can be found with strange tales 358 00:20:01,542 --> 00:20:05,792 that modern-day descendants of the Maya still tell to this day. 359 00:20:05,917 --> 00:20:09,875 RUSSELL: We've investigated dozens of cenotes across the site. 360 00:20:10,083 --> 00:20:13,292 There's several dozen within the city walls of Mayapan. 361 00:20:13,458 --> 00:20:17,792 But we began to hear stories about, you know, the cenote 362 00:20:18,000 --> 00:20:19,333 that was outside of the city wall 363 00:20:19,542 --> 00:20:21,167 that seemed to be kind of deliberately excluded. 364 00:20:22,208 --> 00:20:26,250 There's several kind of stories I was hearing about Sac Uayum. 365 00:20:26,417 --> 00:20:28,833 It's guarded by this... this important 366 00:20:29,042 --> 00:20:30,375 and-and powerful being, 367 00:20:30,583 --> 00:20:33,667 that it was protected by a feathered serpent. 368 00:20:33,875 --> 00:20:35,958 That people had seen the feathered serpent 369 00:20:36,083 --> 00:20:38,625 up in the trees and watched it kind of fly up in the air 370 00:20:38,750 --> 00:20:41,583 and dive down into the cenote when they approached. 371 00:20:43,708 --> 00:20:47,292 SHATNER: In 2013, anthropologist Bradley Russell and his team 372 00:20:47,458 --> 00:20:51,625 prepared to learn more about this storied cenote 373 00:20:51,792 --> 00:20:56,458 and its hidden secrets, and descended into Sac Uayum. 374 00:20:56,625 --> 00:21:00,208 RUSSELL: It's about four stories down to water. 375 00:21:01,708 --> 00:21:03,167 So we knew we were gonna have to rappel in, 376 00:21:03,292 --> 00:21:06,833 get in the water, dive. 377 00:21:07,000 --> 00:21:09,667 And we noticed that there was a small opening, 378 00:21:09,875 --> 00:21:13,833 there was a tunnel that would lead us to something. 379 00:21:13,917 --> 00:21:17,250 So, you know, you went from this large open chamber 380 00:21:17,375 --> 00:21:21,042 into this narrow tube, and then you pass through that, 381 00:21:21,250 --> 00:21:22,583 and it opens up 382 00:21:22,708 --> 00:21:26,667 into this massive beautiful white-walled 383 00:21:26,833 --> 00:21:29,292 gorgeous second chamber 384 00:21:29,417 --> 00:21:31,750 that's filled with water the whole way to the ceiling. 385 00:21:31,875 --> 00:21:34,250 We began to explore that, and we realized 386 00:21:34,417 --> 00:21:36,500 pretty quickly that there were 387 00:21:36,708 --> 00:21:39,625 human remains in the second chamber, 388 00:21:39,792 --> 00:21:43,125 including several skulls that are sitting just completely 389 00:21:43,250 --> 00:21:45,667 face up, staring right at you. 390 00:21:45,792 --> 00:21:49,792 It was unusual because there was no logical way 391 00:21:49,917 --> 00:21:52,125 that you could have put a body in there. 392 00:21:52,292 --> 00:21:54,500 We didn't really understand at first 393 00:21:54,708 --> 00:21:57,042 how there could be human remains in there. 394 00:21:57,208 --> 00:22:00,958 It turns out that the first chamber 395 00:22:01,083 --> 00:22:05,333 sits a little bit above a section of the lower chamber. 396 00:22:05,542 --> 00:22:07,500 And what seems to have happened was that the floor 397 00:22:07,667 --> 00:22:09,417 of the first chamber caved in, 398 00:22:09,542 --> 00:22:12,667 brought down stone in kind of a slope, 399 00:22:12,875 --> 00:22:14,583 and then human remains 400 00:22:14,708 --> 00:22:16,500 that are lighter than the rock settled out. 401 00:22:16,667 --> 00:22:20,458 When we analyzed samples of the human remains 402 00:22:20,625 --> 00:22:22,833 back in the lab, we do a count 403 00:22:23,000 --> 00:22:25,500 that we call the "Minimum Number of Individuals," the MNI. 404 00:22:25,667 --> 00:22:28,000 And the MNI we came away with was, like, 19. 405 00:22:28,167 --> 00:22:29,667 So we know that there's close to 406 00:22:29,833 --> 00:22:32,500 a couple of dozen individuals that are there. 407 00:22:32,667 --> 00:22:34,167 And when we did radiocarbon dating 408 00:22:34,375 --> 00:22:37,125 on their bones that we had across the collection, 409 00:22:37,292 --> 00:22:40,500 they fell consistently about 1350 AD. 410 00:22:40,667 --> 00:22:42,750 We found that it was mixed age and mixed sex. 411 00:22:42,917 --> 00:22:47,042 So, every member of society, essentially, 412 00:22:47,208 --> 00:22:49,042 was represented relatively equally. 413 00:22:50,083 --> 00:22:54,125 HEINERTH: The Mayans considered cenotes as the entryway 414 00:22:54,292 --> 00:22:56,583 to a place they called Xibalba, 415 00:22:56,750 --> 00:22:59,500 which was really their form of the underworld or hell. 416 00:22:59,708 --> 00:23:03,875 So, cenotes were sacred places where, 417 00:23:04,042 --> 00:23:06,042 sure, there were accidental drownings, 418 00:23:06,208 --> 00:23:10,000 but there were also intentional sacrifice rituals, 419 00:23:10,167 --> 00:23:12,583 potentially to seek their gods 420 00:23:12,750 --> 00:23:16,167 to send water in a time of drought. 421 00:23:17,208 --> 00:23:19,250 SHATNER: It's disturbing to consider what may have happened 422 00:23:19,417 --> 00:23:22,542 at Sac Uayum to appease the ancient gods. 423 00:23:22,708 --> 00:23:25,583 But for now, the mystery surrounding 424 00:23:25,708 --> 00:23:29,958 this underwater underground world endures. 425 00:23:30,958 --> 00:23:33,042 RUSSELL: We didn't find any evidence 426 00:23:33,250 --> 00:23:35,250 for decapitation or things that might be 427 00:23:35,375 --> 00:23:37,542 the violence of the actual sacrificial act. 428 00:23:37,708 --> 00:23:41,667 So, we were needing another explanation. 429 00:23:41,833 --> 00:23:45,958 And what we've concluded is that 430 00:23:46,125 --> 00:23:49,083 there was probably a series of disease outbreaks 431 00:23:49,208 --> 00:23:52,750 around 1350 AD, 432 00:23:52,917 --> 00:23:56,542 and somebody needed to deal with the bodies quickly en masse. 433 00:23:56,708 --> 00:23:59,500 And people chose cenote Sac Uayum 434 00:23:59,667 --> 00:24:02,125 to put the bodies into. 435 00:24:02,292 --> 00:24:04,500 So the mystery of why they're there is 436 00:24:04,625 --> 00:24:07,833 slowly being clarified, 437 00:24:08,000 --> 00:24:09,833 but I would never say at this point 438 00:24:09,958 --> 00:24:12,667 that we're 100% certain that that's what it is. 439 00:24:14,667 --> 00:24:17,292 Could a pathway to the underworld really exist 440 00:24:17,458 --> 00:24:19,333 in the watery caves of Mexico? 441 00:24:20,375 --> 00:24:23,667 Given their history, it seems like a chilling possibility. 442 00:24:23,833 --> 00:24:27,583 But there's another cave, this one man-made, 443 00:24:27,708 --> 00:24:30,458 that is said to have been intentionally created 444 00:24:30,625 --> 00:24:34,417 as a place to worship the Devil. 445 00:24:42,250 --> 00:24:44,875 SHATNER: One of the most powerful political figures in Britain, 446 00:24:45,042 --> 00:24:46,917 Sir Francis Dashwood, 447 00:24:47,083 --> 00:24:49,833 commissions the excavation of a quarter mile 448 00:24:50,042 --> 00:24:52,167 of tunnels and chambers 449 00:24:52,375 --> 00:24:56,583 that extend 300 feet below his property. 450 00:24:57,625 --> 00:25:01,583 These man-made caves would soon serve as the meeting place 451 00:25:01,708 --> 00:25:05,375 for Dashwood's enigmatic secret society 452 00:25:05,542 --> 00:25:07,458 known as the Hellfire Club. 453 00:25:08,458 --> 00:25:10,208 Their underground headquarters 454 00:25:10,375 --> 00:25:14,792 would be aptly named the Hellfire Caves. 455 00:25:15,875 --> 00:25:18,458 The Hellfire Caves are quite a mysterious place. 456 00:25:18,667 --> 00:25:20,042 You know, they're subterranean. 457 00:25:20,208 --> 00:25:23,583 They go under West Wycombe Hill about 300 feet. 458 00:25:24,583 --> 00:25:27,000 When one enters into Hellfire Caves, 459 00:25:27,208 --> 00:25:28,792 the first thing you see 460 00:25:28,958 --> 00:25:33,042 is the great gothic facade on the entrance, 461 00:25:33,250 --> 00:25:35,542 and that kind of really sets the tone of this darkness 462 00:25:35,708 --> 00:25:37,042 and mysterious nature. 463 00:25:38,708 --> 00:25:43,000 And as you come further down into the cave network, 464 00:25:43,167 --> 00:25:47,250 there's very narrow passageways, very narrow doorways. 465 00:25:48,583 --> 00:25:50,625 And then all of a sudden, you find yourself 466 00:25:50,833 --> 00:25:54,542 in areas such as this central cavern, 467 00:25:54,708 --> 00:25:58,500 which are very ornate and very kind of precise and deliberate. 468 00:25:59,708 --> 00:26:02,500 You do get that sense of mystery and myth 469 00:26:02,708 --> 00:26:04,125 and legend going on here. 470 00:26:05,083 --> 00:26:06,833 So, here we are in the banqueting hall 471 00:26:07,042 --> 00:26:09,375 of the Hellfire Caves, and as the name suggests, 472 00:26:09,583 --> 00:26:11,625 this is where the Hellfire Club members 473 00:26:11,708 --> 00:26:13,500 would've wined and dined 474 00:26:13,708 --> 00:26:16,333 before their other activities later in the evening, 475 00:26:16,500 --> 00:26:18,833 such as ceremonies and rituals. 476 00:26:19,833 --> 00:26:23,583 The Hellfire Clubs were these extraordinary secret societies 477 00:26:23,750 --> 00:26:26,500 in the 18th century that were set up 478 00:26:26,667 --> 00:26:30,500 by, basically, the cream of society. 479 00:26:30,708 --> 00:26:33,750 At these secret society meetings, 480 00:26:33,917 --> 00:26:34,833 they're questioning the monarchy, 481 00:26:35,042 --> 00:26:36,708 they're questioning the church, 482 00:26:36,875 --> 00:26:39,833 they're questioning old, established ideas. 483 00:26:40,042 --> 00:26:43,500 They were worshiping pagan gods. 484 00:26:43,708 --> 00:26:48,250 And so, Dashwood creates a really extraordinary 485 00:26:48,417 --> 00:26:50,667 venue for these meetings. 486 00:26:50,875 --> 00:26:52,333 SIR EDWARD DASHWOOD: It was secretive. 487 00:26:52,500 --> 00:26:54,000 It was certainly exclusive. 488 00:26:54,208 --> 00:26:55,833 And the sort of membership that went there 489 00:26:56,000 --> 00:26:57,875 and were members were people like 490 00:26:58,042 --> 00:27:01,000 Lord Sandwich, who was First Lord of the Admiralty. 491 00:27:01,208 --> 00:27:03,958 Today, he'd be the equivalent of the Minister of Defense. 492 00:27:04,167 --> 00:27:05,500 You had Thomas Potter, 493 00:27:05,667 --> 00:27:07,458 who was the Archbishop of Canterbury's brother. 494 00:27:07,625 --> 00:27:09,000 Benjamin Franklin visited. 495 00:27:09,125 --> 00:27:10,458 I wouldn't know if he was a member, 496 00:27:10,625 --> 00:27:12,292 but he certainly visited the club. 497 00:27:12,458 --> 00:27:16,167 And then you had my ancestor, as well, Francis of Wycombe. 498 00:27:16,250 --> 00:27:18,458 And Sir Francis Dashwood was definitely an intellectual, 499 00:27:18,625 --> 00:27:20,792 and he always felt there was some 500 00:27:20,958 --> 00:27:23,792 better meaning behind religion. 501 00:27:25,208 --> 00:27:28,667 SHATNER: What was Sir Dashwood and other members of high society 502 00:27:28,833 --> 00:27:33,333 doing in the dark, 300 feet below the ground? 503 00:27:33,500 --> 00:27:36,292 While it's been a matter of debate for hundreds of years, 504 00:27:36,500 --> 00:27:40,500 many believe the long, secret parties 505 00:27:40,625 --> 00:27:43,000 may have descended into something much darker 506 00:27:43,167 --> 00:27:45,625 and more disturbing. 507 00:27:45,792 --> 00:27:48,750 So what went on at these Hellfire Club meetings? 508 00:27:49,792 --> 00:27:51,708 They essentially engaged in 509 00:27:51,917 --> 00:27:56,292 a lot of blasphemy, fornication and gambling. 510 00:27:56,417 --> 00:27:59,875 They dressed up as monks and bishops and essentially 511 00:28:00,042 --> 00:28:02,667 mocked organized religions 512 00:28:02,833 --> 00:28:06,667 through holding satanic pagan rituals 513 00:28:06,833 --> 00:28:09,125 behind closed doors. 514 00:28:11,125 --> 00:28:13,208 -Were people sacrificed? -(woman screaming) 515 00:28:13,375 --> 00:28:15,917 Were people killed down there? 516 00:28:16,042 --> 00:28:18,000 Those who spoke about what they'd seen 517 00:28:18,208 --> 00:28:22,000 talked about the Devil himself chairing those events. 518 00:28:22,208 --> 00:28:26,417 There was a lot of talk of devils being present. 519 00:28:27,792 --> 00:28:30,625 In amongst these claims and counterclaims 520 00:28:30,792 --> 00:28:32,000 about what happened, 521 00:28:32,167 --> 00:28:33,917 there's a lot that's unexplained. 522 00:28:36,708 --> 00:28:39,083 So, here in the cave network, there are loads of 523 00:28:39,208 --> 00:28:41,667 inscriptions in the wall depicting these kinds of faces. 524 00:28:41,875 --> 00:28:44,208 Some of them are said to represent ghosts, imps, 525 00:28:44,375 --> 00:28:46,875 things like that, these mythological creatures. 526 00:28:47,042 --> 00:28:49,833 Some have suggested that these are actually satanic in nature. 527 00:28:50,000 --> 00:28:52,458 We'll never truly know what the artist fully intended 528 00:28:52,625 --> 00:28:55,167 when depicting these, but there are some great examples 529 00:28:55,375 --> 00:28:57,833 all throughout the network of faces just like this. 530 00:28:59,125 --> 00:29:00,750 SHATNER: Was the Hellfire Club really engaged 531 00:29:00,917 --> 00:29:03,417 in dangerous satanic rituals? 532 00:29:03,583 --> 00:29:06,458 Or were they just bored aristocrats 533 00:29:06,625 --> 00:29:09,333 enjoying outrageous drunken parties? 534 00:29:09,500 --> 00:29:12,458 While it's impossible to say, 535 00:29:12,583 --> 00:29:15,750 perhaps the truth lies within the most secretive chamber 536 00:29:15,917 --> 00:29:20,708 of the Hellfire Caves called the Inner Temple. 537 00:29:20,917 --> 00:29:22,083 DASHWOOD: There are a series of tunnels 538 00:29:22,208 --> 00:29:24,917 going 500 meters underground, 539 00:29:25,083 --> 00:29:28,167 going downhill all the way and you come to a river 540 00:29:28,333 --> 00:29:30,500 and an inner temple right at the bottom. 541 00:29:31,708 --> 00:29:33,083 And the whole conceit of this river 542 00:29:33,250 --> 00:29:35,042 is that it's meant to be the River Styx, 543 00:29:35,208 --> 00:29:37,000 which, if you know from your mythology, 544 00:29:37,208 --> 00:29:39,333 separates the real world from the underworld. 545 00:29:39,542 --> 00:29:41,750 There's a bridge there now, but in the old days 546 00:29:41,917 --> 00:29:43,792 there was a proper separation, 547 00:29:43,958 --> 00:29:46,542 and there was a boat that took you across. 548 00:29:46,708 --> 00:29:48,250 It might have only been two or three meters, 549 00:29:48,417 --> 00:29:51,000 but it was this whole narrative that you are now entering 550 00:29:51,208 --> 00:29:52,917 the inner temple, or the underworld 551 00:29:53,042 --> 00:29:54,750 as it was meant to be. 552 00:29:56,042 --> 00:29:57,542 DARKWOOD: The Inner Temple of the Hellfire Caves 553 00:29:57,708 --> 00:30:01,583 is literally as far as you can go within the cave network, 554 00:30:01,708 --> 00:30:03,917 and as far as the Hellfire Club is concerned, 555 00:30:04,042 --> 00:30:07,083 it was the most secretive chamber of the cave network. 556 00:30:07,250 --> 00:30:10,458 Only the most elite members of the club had access 557 00:30:10,667 --> 00:30:11,875 to the Inner Temple. 558 00:30:12,917 --> 00:30:16,500 DASHWOOD: There's a lot going on that we probably will never know. 559 00:30:16,708 --> 00:30:18,625 It was through, really, the 19th century, 560 00:30:18,792 --> 00:30:20,833 so a hundred years later, 561 00:30:20,958 --> 00:30:23,125 that the stories of sort of devil worshiping 562 00:30:23,333 --> 00:30:25,833 and black magic really came to fall. 563 00:30:26,000 --> 00:30:28,458 And we can't prove or disprove them. 564 00:30:28,625 --> 00:30:31,208 How far it went, we don't know. 565 00:30:34,417 --> 00:30:36,750 The Hellfire Club's fascination with the devil 566 00:30:36,958 --> 00:30:38,667 and the disturbing rituals 567 00:30:38,875 --> 00:30:41,333 performed in their subterranean lair 568 00:30:41,500 --> 00:30:45,542 are further examples that the underworld 569 00:30:45,708 --> 00:30:48,333 is a perfect place to hide secrets. 570 00:30:48,458 --> 00:30:52,917 Which is the case with an underground reservoir 571 00:30:53,042 --> 00:30:56,000 in Turkey that some believe once served 572 00:30:56,208 --> 00:31:02,208 as the tomb of the mythical monster known as Medusa. 573 00:31:09,500 --> 00:31:11,500 SHATNER: For thousands of years, this ancient city served 574 00:31:11,667 --> 00:31:14,667 as the capital for the Roman, 575 00:31:14,792 --> 00:31:18,375 Byzantine and Ottoman Empires. 576 00:31:19,542 --> 00:31:22,667 And evidence of these once mighty civilizations 577 00:31:22,833 --> 00:31:25,667 can be witnessed in the architectural wonders 578 00:31:25,833 --> 00:31:27,500 that still exist today. 579 00:31:28,708 --> 00:31:31,167 But deep below the city's surface 580 00:31:31,333 --> 00:31:33,000 lies one of the most mysterious 581 00:31:33,167 --> 00:31:35,333 ancient structures in the world... 582 00:31:36,375 --> 00:31:40,708 ...the Basilica Cistern built in the 6th century AD 583 00:31:40,875 --> 00:31:44,125 by the Byzantine Emperor Justinian. 584 00:31:45,333 --> 00:31:49,667 The Basilica Cistern is the best preserved 585 00:31:49,875 --> 00:31:52,250 underground cistern probably in the world. 586 00:31:52,417 --> 00:31:57,833 A cistern is a water storage container of varying sizes 587 00:31:58,000 --> 00:32:01,125 and the aqueduct that fed the Basilica Cistern 588 00:32:01,292 --> 00:32:04,333 spread throughout the water systems of the city. 589 00:32:04,542 --> 00:32:06,833 So, what we're seeing above the city 590 00:32:07,042 --> 00:32:08,667 in these grand constructions... 591 00:32:09,708 --> 00:32:14,125 ...is mirrored below the city in these underground features. 592 00:32:14,250 --> 00:32:16,667 And so, the water would then be piped 593 00:32:16,875 --> 00:32:18,333 into the Great Palace, 594 00:32:18,500 --> 00:32:20,167 into fountains 595 00:32:20,333 --> 00:32:23,292 and water was channeled through the city. 596 00:32:24,375 --> 00:32:26,333 The cistern that we're talking about 597 00:32:26,500 --> 00:32:29,708 was located at a very low level of the city 598 00:32:29,875 --> 00:32:33,000 and was unknown for many, many centuries. 599 00:32:33,167 --> 00:32:37,208 There's something very magical about descending into a cistern 600 00:32:37,375 --> 00:32:40,833 and seeing the columns around you 601 00:32:41,000 --> 00:32:44,375 and having that firsthand connection 602 00:32:44,542 --> 00:32:47,542 with places that we were never meant to enter. 603 00:32:49,417 --> 00:32:54,167 RYAN: The most unexplained aspect of the cistern is its beauty. 604 00:32:54,333 --> 00:32:57,333 There was no reason to make this utilitarian space 605 00:32:57,500 --> 00:33:00,167 that no one would ever see look like a palace. 606 00:33:00,375 --> 00:33:01,333 And they did. 607 00:33:02,625 --> 00:33:06,125 It is supported by 336 columns. 608 00:33:06,292 --> 00:33:08,083 They are marble and granite. 609 00:33:08,208 --> 00:33:11,833 And the columns soar overhead to these brick vaults. 610 00:33:12,042 --> 00:33:14,375 The purpose of a cistern is straightforward. 611 00:33:14,542 --> 00:33:17,708 But why it's so elaborate, so beautiful 612 00:33:17,875 --> 00:33:20,583 is the greatest mystery of the space. 613 00:33:21,750 --> 00:33:23,875 SHATNER: While the Basilica Cistern's grandeur 614 00:33:24,083 --> 00:33:26,333 is certainly enigmatic... 615 00:33:27,292 --> 00:33:28,792 ...an even greater mystery lies 616 00:33:29,000 --> 00:33:31,750 tucked away in its northwestern corner 617 00:33:31,958 --> 00:33:34,917 where there are two curious columns 618 00:33:35,042 --> 00:33:37,500 supported by massive stones, 619 00:33:37,708 --> 00:33:43,167 skillfully carved to represent the head of Medusa. 620 00:33:43,375 --> 00:33:46,417 GERSTEL: Medusa in ancient Greek mythology 621 00:33:46,625 --> 00:33:48,167 was a significant figure. 622 00:33:48,333 --> 00:33:52,458 She is the daughter of a sea-god... 623 00:33:53,500 --> 00:33:57,917 ...and her hair is made of snakes, that's what you see 624 00:33:58,083 --> 00:34:00,458 when you look at the Medusa heads in the cistern. 625 00:34:00,583 --> 00:34:03,875 Of course, we know that in ancient Greek mythology 626 00:34:04,083 --> 00:34:06,292 she was beheaded by Perseus. 627 00:34:06,458 --> 00:34:11,458 And she had the power in the ancient world 628 00:34:11,583 --> 00:34:15,250 to turn people into stone who gazed at her face. 629 00:34:16,292 --> 00:34:20,833 We often find heads of Medusas associated with temples, 630 00:34:21,000 --> 00:34:24,417 gates of cities or aqueducts. 631 00:34:24,625 --> 00:34:27,833 She's placed in those locations to ward off evil 632 00:34:28,000 --> 00:34:30,417 and to protect those buildings. 633 00:34:30,542 --> 00:34:34,375 For the Basilica Cistern, the Medusa heads, 634 00:34:34,542 --> 00:34:37,667 one might, therefore, ask whether 635 00:34:37,833 --> 00:34:40,333 their placement was intentional, 636 00:34:40,542 --> 00:34:42,292 if there was some reason that they were placed 637 00:34:42,458 --> 00:34:44,292 in a certain part of the cistern. 638 00:34:45,375 --> 00:34:47,583 SHATNER: Were these Medusa heads meant to somehow 639 00:34:47,750 --> 00:34:50,333 protect the city's water supply? 640 00:34:51,208 --> 00:34:52,833 While it's possible, 641 00:34:53,042 --> 00:34:56,083 some believe that the strange orientation of the heads, 642 00:34:56,250 --> 00:35:00,333 with one upside down and one on its side, 643 00:35:00,542 --> 00:35:04,583 may provide directions to a hidden tomb. 644 00:35:06,833 --> 00:35:08,250 As evidence, they point to a document 645 00:35:08,458 --> 00:35:11,000 from the late 19th century, 646 00:35:11,167 --> 00:35:16,000 the diary of Ottoman Sultan, Abdul Hamid II, 647 00:35:16,167 --> 00:35:21,625 where he discloses the cistern's 400-year-old secret. 648 00:35:21,708 --> 00:35:24,167 McMAHON: Many years ago, 649 00:35:24,333 --> 00:35:27,833 the diary of Sultan Abdul Hamid II was discovered. 650 00:35:28,000 --> 00:35:31,458 And in the diary, he makes a reference 651 00:35:31,625 --> 00:35:36,250 to a visit by a delegation from the Republic of Venice 652 00:35:36,375 --> 00:35:38,542 400 years before, 653 00:35:38,750 --> 00:35:42,333 to see the then Sultan of the Ottoman Empire. 654 00:35:42,542 --> 00:35:44,667 These Venetians were able to tell him 655 00:35:44,833 --> 00:35:49,042 where to find the sarcophagus of the Medusa, 656 00:35:49,208 --> 00:35:52,167 which was apparently in the Basilica Cistern. 657 00:35:52,333 --> 00:35:55,250 So, the reason that that head of the Medusa was there, 658 00:35:55,458 --> 00:35:58,167 the statue, was because her body was there 659 00:35:58,375 --> 00:35:59,667 in the Basilica Cistern. 660 00:36:01,292 --> 00:36:04,667 Now the story goes that they did find the sarcophagus. 661 00:36:04,792 --> 00:36:08,167 They opened it up, and the sight inside 662 00:36:08,292 --> 00:36:10,167 was absolutely horrifying. 663 00:36:10,333 --> 00:36:14,625 It was a decaying creature with the head of a human 664 00:36:14,750 --> 00:36:18,208 and a snake's body, and everybody present 665 00:36:18,375 --> 00:36:21,792 was pretty convinced that that was the Medusa. 666 00:36:23,042 --> 00:36:24,083 SHATNER: According to myth, 667 00:36:24,208 --> 00:36:26,333 Medusa was in fact mortal 668 00:36:26,500 --> 00:36:30,542 so it does stand to reason that she died and was buried. 669 00:36:31,958 --> 00:36:33,958 But was the Basilica Cistern, 670 00:36:34,083 --> 00:36:36,792 this magnificent subterranean reservoir, 671 00:36:36,958 --> 00:36:41,167 really an elaborate tomb for this legendary monster? 672 00:36:41,375 --> 00:36:45,458 It's a fascinating claim that at least for now 673 00:36:45,625 --> 00:36:49,792 remains a mystery carved in stone. 674 00:36:50,542 --> 00:36:53,083 GERSTEL: Obviously, the role of the Medusa heads 675 00:36:53,250 --> 00:36:56,542 still needs to be explained, where they came from, 676 00:36:56,708 --> 00:36:59,458 what they're doing there, why they're placed together. 677 00:37:00,833 --> 00:37:02,375 It seems so intentional 678 00:37:02,542 --> 00:37:06,583 as if you are witnessing some underground construction 679 00:37:06,750 --> 00:37:08,667 that may have had another purpose. 680 00:37:08,875 --> 00:37:12,333 But I'm not surprised that the mystery of the space 681 00:37:12,542 --> 00:37:15,917 would give rise to these kinds of stories. 682 00:37:16,083 --> 00:37:17,208 It's just one of the most 683 00:37:17,375 --> 00:37:19,750 spectacular places on the planet. 684 00:37:27,458 --> 00:37:29,375 SHATNER: Since 2014, 685 00:37:29,542 --> 00:37:32,667 mysterious sinkholes that are hundreds of feet wide 686 00:37:32,875 --> 00:37:36,542 have opened up in this remote, frozen landscape. 687 00:37:37,583 --> 00:37:39,625 Over 20 of these deep craters have been discovered 688 00:37:39,833 --> 00:37:43,583 in Siberia's Yamal and Gydan Peninsulas. 689 00:37:43,750 --> 00:37:46,000 And while some have proposed that they are the result 690 00:37:46,167 --> 00:37:51,208 of meteor strikes or even extraterrestrial visitation, 691 00:37:51,375 --> 00:37:55,625 the most recent theory is truly explosive. 692 00:37:57,375 --> 00:37:59,750 The sinkholes in the Yamal Peninsula in Siberia 693 00:37:59,875 --> 00:38:01,375 are formed in permafrost. 694 00:38:01,542 --> 00:38:04,000 Um, and they were all sort of in the neighborhood 695 00:38:04,167 --> 00:38:06,500 of 50 meters deep, about 160 feet deep. 696 00:38:07,708 --> 00:38:10,500 Permafrost is permanently frozen ground. 697 00:38:10,667 --> 00:38:14,500 It occurs in Siberia and Northern Canada. 698 00:38:14,667 --> 00:38:16,542 And in Alaska, in the Arctic regions. 699 00:38:16,708 --> 00:38:18,708 And the permafrost on the Yamal Peninsula 700 00:38:18,917 --> 00:38:22,333 has been frozen solid for about 40,000 years 701 00:38:22,500 --> 00:38:26,042 at least and they can abruptly explode. 702 00:38:27,292 --> 00:38:30,208 So, the sinkholes in the Yamal Peninsula 703 00:38:30,375 --> 00:38:31,750 are formed by a completely different mechanism 704 00:38:31,917 --> 00:38:33,333 from most of the sinkholes that we know about. 705 00:38:33,500 --> 00:38:35,625 The sinkholes are actually these craters 706 00:38:35,750 --> 00:38:39,167 that result from an explosion from below. 707 00:38:39,333 --> 00:38:41,333 They're actually exploding gas craters... 708 00:38:41,542 --> 00:38:43,833 -(explosion) -...and it's somewhat akin to 709 00:38:44,000 --> 00:38:46,417 the popping of a champagne cork. 710 00:38:46,542 --> 00:38:47,833 So, you have this gas on the subsurface 711 00:38:48,000 --> 00:38:49,417 that's causing these explosions. 712 00:38:49,583 --> 00:38:51,083 And that's what's creating those craters. 713 00:38:51,292 --> 00:38:53,167 McGEE: Sinkholes are a phenomenon 714 00:38:53,333 --> 00:38:55,333 that occurs all over the world. 715 00:38:55,500 --> 00:38:57,208 There was the famous example in Guatemala 716 00:38:57,375 --> 00:39:00,625 in the-the center of a street intersection 717 00:39:00,792 --> 00:39:03,833 that was, uh, nearly 300 feet deep. 718 00:39:05,167 --> 00:39:06,667 That's a sudden sinkhole 719 00:39:06,833 --> 00:39:09,625 that could have made a 30-story building disappear. 720 00:39:09,833 --> 00:39:13,333 Sinkholes can be extraordinarily disruptive and dangerous. 721 00:39:13,500 --> 00:39:15,667 So, some can be catastrophic 722 00:39:15,833 --> 00:39:19,000 where there's a sudden failure over a giant cavity 723 00:39:19,125 --> 00:39:22,167 and then a massive hole just makes things disappear. 724 00:39:22,375 --> 00:39:24,792 And others are subtle, slow burns 725 00:39:24,917 --> 00:39:27,292 where there's many indicators on the surface 726 00:39:27,500 --> 00:39:30,917 as things get weaker and subtly start to give way. 727 00:39:31,125 --> 00:39:35,417 And then finally they'll break and you have a giant hole. 728 00:39:35,542 --> 00:39:37,542 There are few things that we can encounter 729 00:39:37,708 --> 00:39:40,750 that attach as much mystery as something like a sinkhole. 730 00:39:40,917 --> 00:39:43,833 Where there was something before, it disappears. 731 00:39:44,042 --> 00:39:45,458 It goes away. 732 00:39:46,458 --> 00:39:48,875 SHATNER: The truth is, we really don't know much 733 00:39:49,042 --> 00:39:53,333 about the hidden dangers lurking just below our feet. 734 00:39:54,583 --> 00:39:57,167 And while there are countless secrets hiding 735 00:39:57,333 --> 00:39:59,833 in the Earth's uncharted underground, 736 00:40:00,042 --> 00:40:01,625 with every new discovery, 737 00:40:01,792 --> 00:40:06,667 it seems the mystery grows even deeper. 738 00:40:06,833 --> 00:40:09,458 There's so much about cave exploration, 739 00:40:09,625 --> 00:40:11,750 so many questions that we're still asking. 740 00:40:12,708 --> 00:40:14,500 I mean, we can learn about animals 741 00:40:14,625 --> 00:40:19,167 that live in completely different ways in the darkness. 742 00:40:19,375 --> 00:40:21,625 We can learn about how ancient cultures 743 00:40:21,792 --> 00:40:24,750 have interacted with these places. 744 00:40:24,917 --> 00:40:28,833 About evolution, survival, future chemical compounds, 745 00:40:29,042 --> 00:40:31,792 pharmaceutical marvels, and so many other things 746 00:40:31,958 --> 00:40:34,125 that we haven't even thought about yet. 747 00:40:34,250 --> 00:40:36,667 So important, important, um, discoveries 748 00:40:36,875 --> 00:40:38,375 are coming from cave environments 749 00:40:38,542 --> 00:40:40,083 and the life within them. 750 00:40:41,125 --> 00:40:42,750 McGEE: The Earth has a way of surprising us. 751 00:40:42,917 --> 00:40:45,208 It would be naive for anyone to say, at this point, 752 00:40:45,375 --> 00:40:48,667 that there are no mysteries left to solve 753 00:40:48,792 --> 00:40:51,042 when it comes to any scientific venture, 754 00:40:51,208 --> 00:40:52,625 not the least of which is, 755 00:40:52,792 --> 00:40:54,542 "What's going on right underneath our feet?" 756 00:40:55,583 --> 00:40:57,500 Exploration under the earth 757 00:40:57,625 --> 00:41:00,125 represents a frontier in many directions. 758 00:41:00,250 --> 00:41:02,167 There's a lot going on down there we don't know about. 759 00:41:03,042 --> 00:41:05,583 As we venture down into the deep, ever farther, 760 00:41:05,750 --> 00:41:09,542 we will start to find the next layer of mysteries 761 00:41:09,708 --> 00:41:12,208 left for us to discover underground. 762 00:41:14,208 --> 00:41:17,167 It is said that 90% of Earth's caves and tunnels 763 00:41:17,333 --> 00:41:21,583 are unexplored and with so many new ones forming every year, 764 00:41:21,750 --> 00:41:24,417 it would seem that the subterranean world 765 00:41:24,583 --> 00:41:28,500 is perhaps far too vast to be fully understood. 766 00:41:28,667 --> 00:41:32,833 Whether it's gigantic caverns, hidden passageways 767 00:41:32,958 --> 00:41:37,167 or massive holes that suddenly appear out of nowhere, 768 00:41:37,375 --> 00:41:43,042 the underworld is constantly revealing new mysteries. 769 00:41:44,292 --> 00:41:47,708 And no matter how deep we go, one thing is clear, 770 00:41:47,917 --> 00:41:50,667 we've really only scratched the surface 771 00:41:50,875 --> 00:41:54,792 of our planet's deepest, darkest secrets 772 00:41:54,958 --> 00:42:00,458 that continue to remain unexplained. 773 00:42:00,583 --> 00:42:02,708 CAPTIONING PROVIDED BY A+E NETWORKS