There’s something inherently spooky about a cave. That’s true even before you add in the possibility of finding something unexpected inside the dark, dank space. These 20 caves crawl with strange critters, hide gory secrets, contain creepy ancient structures or enough toxic gas to kill you if you dare enter. Which ones would you dare enter?
20. Neanderthal-era structures made of stalagmites
The Pyrénées mountains stretch through southwest France and it was in this region that explorers found something strange in the 1990s. Nearly a quarter-mile inside the Bruniquel cave, they discovered structures built from stalagmites. Someone had used nearly 400 of the rocks to create walls across the cave floor. At the time that the cavers found this strange construction, experts estimated they were 50,000 years old – the same age as burnt animal remains found nearby.
However, contemporary estimations say that these stalagmite walls are twice that age – they came to be more than 100,000 years before the first humans made their way to Europe. Experts say it was the Neanderthals who built the weird structures. Archaeologist Marie Soressi told The Guardian in 2016, “This is completely different to anything we have seen before. I find it very mysterious.”
19. Remnants of ancient witchcraft
Rumors have long swirled about the Swedish island of Bla Jungfrun. Some people believe that, if you take a rock from its beaches, you’ll have a lifetime’s worth of bad luck. This and other theories are actually rooted in history, considering what archaeologists have found in the caves on the deserted island.
During a 2014 trip, archaeologists uncovered evidence of sinister Stone Age rituals dating back 9,000 years. Specifically, it appears that ancient people took part in religious rituals — perhaps even witchcraft — in a pair of caves on Bla Jungfrun. Modern-day explorers found an altar and a fireplace, the latter having a hollow wall so that an assembled audience could watch whatever dark practices that took place there.
18. A more-than-one-mile-long drop into the dark
Speleologists – scientists who specialize in studying caves – made their way to Georgia’s Krubera cave in the 1980s. When they arrived, they found a very creepy sight – crows nesting all around the entryway. And yet, somehow, that’s not the scariest part of this geological wonder tucked into the country’s Abkhazia region.
Just past the crows, the Krubera cave drops more than 7,200 feet into the Earth. As such, it’s the planet’s deepest cave. Ukrainian speleologists mapped the expanse in 2001, and they found that the cave ends in a siphon underwater. Alarmingly, it took them two weeks to get down far enough to reach this part of the cave.
17. An underground forest
Traipsing through the Vietnamese jungles in which he lived, a man named Ho Khanh discovered something remarkable in 1991. It was an opening that led into a cave, but he couldn’t explore it himself – only a few steps inside was a 200-foot drop. In 2009, the British Cave Research Association picked up where Ho left off, making their way into the Son Doong Cave.
The five-mile-long cave could fit skyscrapers into some of its larger caverns. And yet, it’s not the size of the Son Doong that its most impressive feature. It also encompasses an untouched jungle that grows over 600 feet underground. The trees and plants can actually thrive here because a portion of the earth overhead has collapsed, letting sunlight into this stunning expanse.
16. A five-foot stalactite called the Crystal King
In 1897 Robert Noffsinger, a farmhand from West Liberty, Ohio, noticed a sinkhole slowly filling up with rainwater throughout a downpour. Somehow, though, all of the water was gone the next day. This led to the discovery of an underground river, which carved out an extensive network of caverns beneath Noffsinger’s feet.
This underground network became Mt. Tabor Cave Tours, a going concern that took the time to remove mud from the far reaches of the Ohio Caverns, lengthening the walkable distance from a quarter-mile to two miles. The biggest treasure discovered in the depths was the so-called Crystal King. This white, nearly five-foot-long stalactite is reckoned to be 200,000 years old.
15. The oldest cave paintings known to man
Just a simple red disk – that’s the painting in Spain’s El Castillo cave that made archaeologists’ jaws drop. That’s because they went on to determine that this basic piece of artwork was probably more than 40,800 years old. Until then, the oldest cave paintings in the world — the Chauvet cave paintings in France — were estimated to be 37,000 years old.
Experts weren’t just shocked by the age of this ancient disk painting, though. The timeline opened up the possibility that it wasn’t modern humans who created it — although they did arrive in Europe around 41,500 years ago, allowing them enough time to paint. It is, however, possible that Neanderthals might have been behind the art, which would demonstrate the species’ ability to create and come up with symbolic works.
It’s one thing for explorers to crack open Egyptian tombs and find mummies – there, at least, they are to be expected. In the Philippines’ mountains of Kabayan, though, so-called “fire mummies” were scattered throughout the caves. And those who laid them to rest didn’t mummify them in the traditional way.
The Fire Mummies of the Philippines prepared for their internment by downing a salt-laden drink just before the end. Then, once they passed, the living would smoke the dead bodies over fire to activate the salt in their stomachs. The heat-and-salt combination then pushed fluids from the bodies, which has kept them preserved for 800 years and counting.
13. Two million bats
A single bat swooping through the sky can be scary enough. Now, imagine two million of them flocking together and taking off into the night. You can see it for yourself, if you wish, on Samal Island in the southern Philippines, where the world’s largest population of Geoffrey’s rousette fruit bats reside in the Monfort Bat Cave.
All two million of these megabats — as they are sometimes known — reside within the 245-foot cave, the only one that’s protected on Samal Island. There are more than 70 such caverns on the island, and experts have found evidence that large groups of bats once lived within them, too. In other words, the island used to be home to far more of the winged mammals, an even creepier thought.
12. An underground graveyard of ancient giant lemur bones
Madagascar’s Aven Cave in Tsimanampetsotsa National Park may be filled with water, but that hasn’t stopped paleontologists and divers from exploring it. And their missions into the depths have yielded some incredible finds. The silt-covered floor of the cave is littered with the bones of extinct, exotic animals, with the giant lemur being the most prevalent among them.
These massive lemurs – which were nearly the size of modern-day gorillas – disappeared, likely at the hand of human hunters around 2,000 to 5,000 years ago. However, the skeletons preserved in the Aven Cave have given experts a much more detailed glimpse at what they were like. It appears the animals were left to naturally decompose, so their skeletons are in pristine condition, even if they are underwater.
11. Ancient teeth, which points to the extinction of a human-hobbit species
Researchers discovered a new species in Indonesia in 2003 called the Homo floresiensis, and the one-meter-tall beings confused them. They carbon-dated these uncovered “hobbit” remains to approximately 11,000 years ago. This timeline would signify that they had coexisted with modern humans for thousands of years, which scientists couldn’t see happening.
However, in 2016, researchers found further evidence to clarify the story. In a cave on the Indonesian island of Flores, where the hobbits once lived, they uncovered a pair of human teeth. The 46,000-year-old chompers put humans on-site, and updated dating techniques placed the hobbits’ extinction to about 50,000 years ago. From there, experts could say that the two species were likely to have interacted – but, to what extent, no one can say.
10. The largest selenite crystals known to man
A pair of miners had specific instructions as they dug into the earth beneath Mexico’s Naica mountain in 2000. They were there to carve out a tunnel for a company called Industrias Peñoles. But, as they cut through the earth, they found something stunning – a cave stuffed with massive gypsum crags, some measuring up to 36 feet in length.
In 2007 geologist Juan Manuel García-Ruiz and a research team studied the translucent shards in the aptly named Cave of Crystals to see how they formed. The experts examined fluids tucked into the rock, which revealed that the crystals formed in mineral-rich water. Specifically, the mineral anhydrite dissolved into gypsum, which took on the same shape as the stunning formations we see today.
9. Spiders the size of a softball
It’s hard to believe that anyone would go into a cave in the hope of finding a massive spider. However, in 2017 San Diego Natural History Museum researchers Jim Berrian and Michael Wall helmed multiple expeditions into Baja California to find an elusive, cave-dwelling arachnid whose exoskeleton they had discovered four years prior.
Wall told the Los Angeles Times that the softball-sized arachnid was “the type of spider that a lot of people would shriek and run from”. But for him and Berrian, it was easy to forge ahead, as they had actually discovered a new species. The tarantula-sized creepy-crawler had fangs, hair, an inch-long body and four-inch legs – not the type of creature you’d want to meet in a dark cavern.
8. Seemingly endless tunnels
It’s terrifying to even think of getting lost in an underground cave. However, that could very easily happen in Kentucky’s Mammoth Cave. Explorers have so far mapped 365 miles of subterranean passageways, but they haven’t seen all of it – and they have no idea just how large the network is. They still continue to uncover new recesses and caverns, though.
Now a huge tourist attraction, nearly 400,000 people visit the limestone cave in Mammoth National Park every year. However, the first person to descend into its depths did so more than 4,000 years ago – and exploring the winding underground tunnels had to be especially creepy for the first-ever visitor.
7. Evidence of human decapitations
Scotland’s Sculptor’s Cave takes its name from the symbols etched into the rocks that surround its entrance. Experts have linked these carvings to the Pictish people, who added their designs between 500 and 600 AD. However, their creations weren’t merely decoration – they etched them there as a warning of the dark practices that happened within.
The Picts weren’t the ones responsible for the cave’s gruesome reputation, though. During the Late Bronze Age – which stretched from 1200 to 500 BC – the natural alcove was the site for funeral practices. And there’s evidence that around 250 BC at least six decapitations took place there, all part of the same gory ceremony – perhaps executions or human sacrifices.
6. Dripping slime
Walking into a dark cave is already a scary leap of faith. But imagine walking inside, shining your flashlight onto the walls and seeing them ooze with a thick slime. Researcher Diana Northrup discovered a pulsating, gooey substance sliding down a the walls of a cave in Tabasco, Mexico — but, surprisingly, she wasn’t spooked.
Instead, Northrup and her colleague, Penny Boston, considered the slimy substance to be an incredible feat of evolution. Indeed, cave-dwelling bacteria often form a gooey “biofilm” to protect themselves from environments where toxic elements like sulfuric acid fills the air. As Boston explained to the NASA.gov website in 2003, “It acts as a place for them to conduct their own little chemistry labs, so to speak, regardless of what is going on outside of the film.”
5. A 33-foot-long anaconda
Demolition crews often rely on explosives to help them in their work. Indeed, a stick of dynamite can speed up process the and make it safer and more controlled for laborers. However, when workers lit the fuse to blast the Cave of Altamira in Para, Brazil, there was one unforeseen obstacle that no one could have predicted.
After detonating the explosives, the crew found an 882-pound, 33-foot-long anaconda slithering through the cave. Creepy footage of the reptile exists and pans down its sprawling body, highlighting its impressive 39-inch diameter. Unfortunately, unconfirmed reports claim that the crew ultimately killed the snake instead of returning it to its natural habitat.
4. Phosphorescent worms
In 1887, an English surveyor named Fred Mace enlisted the help of Maori Chief Tane Tinorau to explore the New Zealand landscape. The pair boarded a small raft and paddled into an underground cave, and, as they navigated the dark expanse, they noticed that their candles weren’t the only thing giving off light.
It turned out that thousands of glowworms dangled from the roof of the cave, mimicking the gentle glow of stars overhead. Both explorers were in awe of their discovery, and they made frequent trips back to explore the glimmering cave. Nowadays, tourists do much the same, boarding boats to glide into Waitomo Glowworm Caves, to see the stunning spectacle created by insects.
3. Satanic statues
Not all caves are naturally formed. Case in point: the Hellfire Caves in West Wycombe in England. A group of wealthy pagans, the Hellfire Club etched out a series of subterranean tunnels and rooms in the 1770s. They required a place to conduct their mostly indulgent — often sinister — business, which ranged from tipsy toasts to orgies and sacrifices.
The Hellfire Caves became a tourist attraction in the early 1950s – and are still a popular destination. As tourists traipse through the labyrinth, they’ll see some very creepy statues carved into the subterranean meeting space. Specifically, there is at least one figure that appears to be Satan.
2. Salt-preserved men
Iranian miners have toiled in the Chehrabad Salt Mine for years and — more than a few times, now — they have found more than just the white mineral. In 1993 they discovered a nearly perfectly preserved mummy from 300 AD, complete with a lengthy snow-colored beard and a gold bauble in his ear.
Other mummies — equally as well preserved — have popped up since then, including one that was more than 10,000 years old. All of them have remained in near-perfect condition because of the dryness and saltiness within the cave. In fact, it’s such a dry environment that some of the mummies still have their internal organs intact, thousands of years after their deaths.
1. Lethal levels of sulfur
No one knew about the Movile Cave in Romania until workers stumbled upon it while scouting for a suitable location for a power plant. Since then, less than 100 people have explored this creepy expanse, partly because it is so dangerous simply to enter. Lone explorers have to descend 65 feet through a narrow shaft, then fumble their way through a pitch-black passageway into an underground cavern, complete with a lake.
Once a person reaches the so-called lake room, they have to be wary of breathing it in for too long. Dangerous gases, including carbon dioxide and hydrogen sulphide, hang in the air. Plus, there’s less oxygen than you’d find normally. After only about five or six hours, your kidneys would begin to fail – which explains why so few people have made the descent to see this weird underground environment.