A U.S. National Natural Landmark in southern Indiana, discovered in 1883 by two children who crawled in with a candle. It is famous for the delicacy of its formations, thin soda-straws, flowstone and reflecting pools, and stays a constant 52 degrees. PUBLIC guided tours (a walking tour and a longer one), Crawford County, Indiana.
Indiana
See it on the map
Other places on the map within a couple of hours.