The Hidden World Below: 23 Surprising Facts about Caves

In the Blue Lake Rhino Cave in Washington State there is a 14.5 million-year-old cast of an early Rhino ancestor about 300-feet up the side of a cliff, which was created when basalt lava slowly covered the corpse floating upside down in an ancient lake.

Three Boys explored a small cave (Lummelunda Cave) in Sweden using matches and planks every Sunday. After regularly exploring for two years, in 1948, a stone fell and opened a passage into a much larger cave system. The first hall after the passage was named “The Mountain King’s Hall.”

The Giant Crystal Cave in Mexico, with crystals weighing up to 50 tonnes, had an average of 100% humidity and 58°C temperature. This meant that the coldest place in the cave was the lungs, so water would condense in it, and exposure for over 10 minutes would lead to death by drowning.

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.

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.

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.”

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.

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.

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."