The largest and most well-preserved petroglyph site in the Verde Valley.

Cave where bat-eating snakes hang down from the ceiling.

Home of a 28-foot tall stalagmite known as the War Club.

Mile-long cave system near Great Smoky Mountains.

These sub-farmland caves are home to a majestic stalactite known as the "Crystal King."

The mysterious wonder of an underground waterfall is illuminated by multicolored lights.

An ancient cave system in Tennessee’s Appalachian foothills converted to a 1,200-person music venue.

The world's longest known cave system.

148 feet long and in the middle of a verdant forest.

Home of an evil witch famous within southern folklore.

This cave holds a surprisingly colorful variety of geological oddities.

This large midwestern cavern features impressive rock formations and an underground waterfall.

Inside this mountain lies several kilometers of breathtaking caves.

Abandoned railroad tunnel is home to a colony of three million Mexican free-tail bats.

This sacred cavern, 400 feet deep, is home to millions of bats and an ancient burial ground.

A Texas cave network is home to some of the world's most spectacular-looking and bizarrely named mineral formations.

The longest continuous lava tube in the continental U.S. offers 2.5 miles of dark explorations for the adventurous.

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

The longest continuous lava tube in Oregon.

In the middle of a suburban Denver neighborhood is a cave that once provided solace for a prominent Ute chief and his family.

A small metropolis of Pueblo cave dwellings have been carved right into the hillside of this national monument.

A frozen oasis lies beneath the scorching New Mexico desert.

Limestone caves with spectacular showcase chambers.

Its dark depths conceal millions of rare, delicate crystal formations.