The longest navigable underground river in the United States is home to countless blind and albino animals.

The longest living non-clonal organisms on Earth.

This bird-shaped rock formation defies gravity, time, and classification.

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

Bizarre lunar-like landscape with thousands of large stone "hoodoos."

European castle ruins in an American state park are actually the product of death and grief.

This Big Sur waterfall drops 80 feet directly into the Pacific Ocean, and inspired the hillside house up top.

An unfortunate geological resemblance to Satan has labeled this Pasadena gorge as a passage to the underworld.

This rugged area of red rocks and arches is often considered one of the most beautiful places on Earth.

A castle built by an eccentric medieval enthusiast in rural Ohio.

Eons old volcanic activity created one of the most stunning rock formations in the United States.

Stripes of flowers bloom each spring in a 50 acre rainbow of color.

Giant, natural amphitheaters made of delicate geological formations called "hoodoos."

This woodland architectural installation acts as a camera obscura for the heavens.

Strange red rock formations that have been attributed to a higher power for hundreds of years.

If drivers cross the rumble strip on this stretch of Route 66 at just the right speed it plays "America the Beautiful."

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

Ninety feet off the valley floor is an ancient dwelling put under protection of the U.S. government by Teddy Roosevelt.

The largest earthwork effigy in the world.

The largest self-built castle in the U.S., six decades in the making.

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

The hike through a narrow river flanked by the 2,000-foot-tall walls of Zion Canyon is one of the best in the world.

The land is full of geologic eye candy, such as otherworldly spires, mushroom-shaped hoodoos, and prehistoric fossils.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.