More than five miles of underground passageways.

The highest point in Alabama was almost completely deforested, but is now home to protected towers and trees.

The Grand Canyon of Texas.

An immersive environment that is part haunted house, part choose-your-own-adventure, and part jungle gym.

A natural formation that resembles a camel resting in the New Mexico desert.

The state bird of New Mexico, constructed entirely out of garbage.

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

This is one really big nut.

Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

Twenty-seven massive radio antennas on the high plains of New Mexico search for life on other planets.

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

The 7,000-year-old calcium carbonate formation creates a magnificent natural bridge.

Legends surround this jagged rock formation in the New Mexico desert.

Seemingly grown on some other world, these New Mexico rock formations look like a disused science fiction set.

These aggressively sustainable art homes look like something out of 1970's science fiction.

This volcano rises like a giant anthill from the plains below, with a road spiraling up to the rim.

Historic, 19th-century wagon wheel ruts cut into soft volcanic ash.

Unlike most arches, this geological oddity formed in a volcanic dike.

An antique narrow gauge railway line still running through the Colorado and New Mexico mountains.

The ancient dwellings of the Puebloans, located in the cliffs of majestic mesas.

The marker offers a rare chance to be in four U.S. states at once, though there's some controversy over its geographic accuracy.

A river runs through this remote valley in a very unexpected way.

Community owned and operated, this property is home to a diverse set of nudists.

Climb to the top of this spiritual tower, and you'll be rewarded with spectacular views.