Mighty Cold and Dark

Before going into "Hole of the Devil," for example, Boyer puts on long underwear and other extra clothes. Then, he wades into a stream and squeezes through a small opening in the cave. The lamp on his helmet gives off light by burning a smelly gas called carbide.

Without this light, the cave would be pitch black. But that hasn't stopped some animals from doing some caving of their own. Bats, which actually live in the caves, use sonar―a way of using sound to guide themselves.

Other animal visitors to the cave, including salamanders, foxes, and raccoons, smell their way around.

There are no fish in the cave's streams, but there are tiny wriggling creatures called flatworms. Earthworms can also be found there―survivors of long drops into the cave. Cows, too, have fallen into caves, but farmers rescue them.