Only Gypsum Show Cave in the U.S.
Freedom, Oklahoma
Set in a 200-acre state park, Alabaster Caverns is, in fact, made of alabaster, a rare form of gypsum. It's the only gypsum show cave in the U.S. and the largest natural gypsum cave in the world open to the public.
Steep steps lead into a hole in the ground; guides lead you on a three-quarter-mile tour enhanced with five species of bats -- the cave was originally called Bat Cat -- translucent sheets of selenite rock, and colorful lighting designed by a guy from the National Air and Space Museum. Outside, there's a good stick-your-head-here-and-be-a-cave-bat photo-op.