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

It would take 35 firetrucks to fill this enormous glacial pothole.

According to local lore, this narrow passageway through two large rocks was accidentally created by the devil himself.

A curious whirlpool formation supposedly capable of entangling or engulfing branches, tree trunks, or whole rafts full of hapless tourists.

An improbable waterfall springs from an orange-white cliff face, tumbling into the headwaters of the Virgin River above Zion National Park.

Who needs fancy modern water slides when this giant North Carolina rock works just as well?

Rippling sand dunes frozen in the Arizona rock.

Dramatic river bend surrounds a natural red-rocked pedestal.

This quiet park's strange sedimentary spires were named after Kodak's color film.

A preserved stretch of ancient fossilized trees with an impressive gem collection to boot.

A frozen oasis lies beneath the scorching New Mexico desert.

This maze-like slot canyon is a unique gem within an already fascinating geological area.

This freshwater spring fills with 10,000 gallons of water per minute.

Half of a waterfall goes into the river while the other half seems to disappear.

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

A subterranean world of tunnels links several buildings of this rare 19th-century asylum.

This cave holds a surprisingly colorful variety of geological oddities.

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

The "World's Largest Underground Business Complex," a 55,000,000-square-foot city underneath Missouri.

Chilly air billows out from the entrance of an abandoned mine on a steep hillside, providing a refuge for Ice Age fauna and flora.