Breathtakingly blue walls shimmer inside the "Glacier Behind the Town."

At this Denver landmark, the meals are compulsory, the sopapillas are complimentary, and the insanity is everywhere.

Hundreds of glow-in-the-dark objects light up a museum in a historic zinc mine.

An abandoned stretch of highway, deteriorating next to the operational one.

Collapsing castle on the Hudson river was once the storage site of military surplus business.

No one knows how this Pacific Northwest spruce tree came to have so many trunks.

Wild lights and sound effects turn a walk through some caves into an eye-popping 1960s tourist attraction.

Quite simply the largest tree in the world (by volume).

This symbolic piece of New Orleans architecture is also home to a few ghastly stories.

The scuba diving training facility was named for the steam that rises from the cave's chimney.

Bigfoot prints, Feejee mermaids, and haunted dolls on display in a tiny North Carolina town.

A sacred site for Native Americans surveyed by George Washington and owned by both King George III and Thomas Jefferson.

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

This natural wonder drops 16 stories straight down through rare flora and streaming waterfalls.

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

A modernist landscape of water and sci-fi concrete.

This knobby, drooping New Orleans oak is a favorite place both for climbing and for meeting giraffes.

Frank Lloyd Wright's most iconic home dangles over a Pennsylvania waterfall.

This geothermal hot spring hides beneath a slowly growing mineral dome.

The world's longest known cave system.

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

A DIY art gallery/music venue/lecture hall dedicated to video game culture.

A stunning, two-tiered waterfall made famous by poets, artists and the legend of a ghost dog.

This naturally-sourced hot spring is now home to a clothing-optional resort.