In 1839, Dr. John Croghan bought Mammoth Cave in Central Kentucky and turned it into a tuberculosis hospital. It was a massive failure and Dr. Croghan died of Tuberculosis.
2. An underwater cave named Cosquer Cave in southern France has more than 20,000-year-old cave art on its walls, which were probably made when the sea levels were lower. The art depicts Auks, Bison, wild horses, and more.
3. All of the world's four deepest caves are located in Abkhazia in Georgia. The record-holder is Veryovkina Cave, which goes down at least 1.3 miles. Due to the hazards and need for specialized rope techniques, “the round trip —top to bottom and back— takes professional speleologists about a week.”
4. The oldest known sewing needle is 50,000 years old. In 2016, scientists in Siberia found an ancient sewing needle in a mountain cave. It was made from the bones of a large and unidentified bird.
5. The Cave of Swallows in Mexico is the largest cave shaft in the world, being almost 1,000 feet wide at the bottom and 1,100 feet deep, and it's home of many birds, but despite its name, almost no swallows.
In June 1836, a group of boys in Arthur’s Seat, Scotland found 17 small coffins with tiny dolls inside in a cave. Their origin is still debated but theories include witchcraft, burial superstitions and them being a tribute to the 17 victims of the notorious "body snatcher" serial killers.
7. In 1971, Soviet geologists tapped into a cavern of natural gas. The ground beneath the rig collapsed, leaving a hole 70 m across. To avoid a release of harmful gas, they lit it on fire, thinking it would burn off in a few days. 41 years later it is still ablaze. Locals call it "The Door to Hell."
8. Am-Phu cave in Vietnam is decorated with "hell" themes: sculpted demons "and fanged devils bathed in sinister red light, where hands reach up from the waters below and river monsters threaten to gnash (visitors') souls to bits." It's located under the mountain associated with heaven.
9. The Bracken Bat Cave in Texas has the largest known bat colony in the world. Over 20 million bats live in the cave, which is more bats than there are people living in Mumbai, India, one of the world’s largest human cities.
10. Wolf Cave a.k.a. Susiluola is a cave in Finland which claims to have evidence of Neanderthals living there pre-Ice Age. It is the only known place to have such evidence in Nordic countries.
11Lubang Jeriji Saléh Cave
The oldest known figurative painting was discovered in a cave named Lubang Jeriji Saléh Cave on Borneo island, Indonesia: a depiction of a bull has been dated to be 40,000 years old. It is unknown which species of humans created the paintings and what happened to them.
12. There exists a cavern named Marvel Cave in Missouri that’s so large that in 1994 five hot-air balloons were flown simultaneously inside it.
13. The earliest known modern human fossils found outside of Africa were in Apidima Cave in Southern Greece. These fossils are somewhere between 170,000 and 210,000 years old.
14. Massacre Cave is a cave on a small island in Scotland. When the Clan MacLeod attacked the Island, all 395 of the islanders hid inside the cave. When the MacLeods found them, they made a fire at the cave mouth and allowed the smoke to suffocate everyone inside.
15. The oldest known human-made structure is in the Theopetra cave in Greece. This is a stone wall constructed over 23,000 years ago yet the cave itself was occupied by humans from about 135,000 BC.
There is an underground cave in the Dolomite Mountains in Italy where a Consortium of fruit growers store 40,000 tons of apples inside.
17. While exploring a historic 1900s guana mine, cavers uncovered the largest limestone cave (Lechuguilla Cave) in the United States. Not only did the cave stretch more than 120 miles but it also held a 20-feet gypsum chandelier and rare rock-eating bacteria.
18. There is a cave in England that from the 1500s until 1880 was called "The Devil's A*se". It was renamed as Peak Cavern shortly before Queen Victoria visited for a concert.
19. Ajanta Caves in India are 29 caves joined together, which are filled with paintings from over 3 religions (Hinduism, Buddhism, and Jainism), which were constructed in 520 B.C. They cave system is spread over an area of 8,242 hectares, making it one of the largest man-made cave structures ever built.
20. The Vrtoglavica Cave in Slovenia has a 600-meter vertical drop, which is the longest such drop in the world.