What Lies Beneath: The world’s longest cave. Over the years, “mummies” of prehistoric cave explorers have been discovered. The first recorded find was in 1935: a six-ton boulder with a body pinned underneath. In the mid-1800s, a doctor who (incorrectly) believed the humid conditions might be a remedy for tuberculosis, turned the cave into a sanitarium.
How Did It Get There: Parts of the 365 miles of the underground caverns started forming from tributaries more than 10 million years ago, and caves continue to form even today. The tunnels’ constant atmospheric conditions, combined with the salty soil and absence of sunlight, preserved the bodies of people who met their deaths below the surface.
Cool Bonus: Stephen Bishop, the cave’s most famous explorer, was brought to the caves in 1938 as a slave. He was the first person to descend all five levels of the cave, 360 feet below the surface, and made the scientific discovery of the eyeless Kentucky cave fish that still swim in the waters today.