Photo: Warren LeMay / CC BY-SA 2.0
Mammoth Cave's ranger tours have easy walks at one end and strenuous crawls at the other, and the Historic Tour follows corridors people have walked since the early 1800s, past Broadway and the Bottomless Pit. One of the tight squeezes is called Fat Man's Misery. It stays 54 degrees down there all year, so you'll want a jacket in July. More than 426 miles of the cave have been mapped, longer than any other known on Earth.
63 placesAll 63, for anyone keeping count, with the famous ones up top and the quieter ones further down.
22 placesThe Park Service runs eight of these 22 caves, and most of the rest are commercial show caves at $23 to $36 an adult. If you only pay for one, make it Ruby Falls: you ride an elevator 26 stories down inside Lookout Mountain and walk to a 145-foot waterfall.
