The largest cave shaft in the world is home to thousands of birds and popular with BASE jumpers.

The show pony of cave systems, Fantastic Caverns manages to live up to its name.

Where there's quartz, there must be gold. Thus is the story of the mines of Julian, and the titillating times of the Gold Rush.

A waterfall 600 ft. inside a mountain, once the bane of gold miners, is now a spectacle of nature.

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

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

An ethereal glowing blue ocean cave in Croatia.

Limestone caves with spectacular showcase chambers.

Enchanting cave with a river crashing through the roof.

Holy Hindu shrine in an enormous, monkey-filled limestone cavern.

Gorgeous cave resemble a winter wonderland.

One of the largest, oldest, darkest, quietest motel rooms in the world.

Home to some of the oldest hominid fossils ever found.

A cave's rare beauty held a cavernous secret hidden underground.

A museum dedicated to the alleged Roswell Incident.