Towering basalt columns, a creation of fire and ice.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.

An artsy hidden staircase leads to breathtaking views of San Francisco.

This tiny movie theater was the last one in the U.S. constructed in the Nuevo Deco architectural style.

This Yellowstone geyser may not shoot as high as the nearby Old Faithful, but it erupts for considerably longer.

A beautiful geyser under environmental threat.

A fitting attraction for the corn capital of the world.

A museum, walk-through diorama, and library nestled under one castle-like roof.

Site of the 1879 Cheyenne Outbreak and the site where famed Sioux chief Crazy Horse met his fate.

Otherworldly rock formations and ancient fossils abound in this unique stretch of Nebraska badlands.

A railroad lift bridge that was only lifted once and became obsolete before construction was finished.

The ruins of Theodore Roosevelt's beloved ranch stand in a forgotten corner of a national park named after him.

One of America's first dinosaur parks gives a window into Depression-era paleontology.

Thanks to a loophole in property ownership, this alleyway has become a cacophonous street gallery.

One of the first intercontinental ballistic missile sites in the United States.

Examine the impact of the horse on Great Plains culture through exhibits on ranching, rodeo, and the Native American way of life.

A six-ton, 12-foot-tall concrete prairie dog is touted as the largest in the world.

Dedicated to the history of the 1,000 nuclear missiles that once covered the Great Plains.

This prehistoric sinkhole lured exclusively male mammoths to their death, much to the delight of science.

The world's largest mountain carving could fit all of Mount Rushmore inside it many times over.

Despite repeated attempts to make it work, this former mining town is now nothing but dust and memories.

The highest point in South Dakota contains the ashes of Valentine McGillycuudy, the "Holy White Man."

The first declared National Monument in the United States.