21. Carlsbad Caverns National Park, New Mexico

Annual visitors: 465,912

Fun fact: Originally explored by Jim White, who descended the caves on a rickety ladder when he was only a teenager.

One of the definitive features of this cave system is the whimsical names of the formations given to it by its young first explorer, Jim White. The Queen’s Chamber, Hall of the White Giant, and Lake of the Clouds can now be accessed by even unseasoned spelunkers. The site has over 110 different caves to explore, some of which have only been recently discovered. A popular spectacle unique to these cave is the Bat Flights, when at dusk the cave’s bat population takes to the air en masse.