An uber-secure, windowless tower of doom in the center of Manhattan is an NSA spyscraper.

Under a glass sidewalk lie the remains of some of Manhattan's oldest buildings.

Local lore holds that Butch Cassidy took an escape route through Red Canyon's sandstone hoodoos after an attempted murder.

Dig for your own trilobites in this goldmine of invertebrates.

Incredible sculptures inspired by obscure passages from the Bible.

Largest collection of mounted dinosaur specimens in the world.

A replica that won't float away.

Largest man-made excavation on earth!

Another of California's unused Cold War missile defense complexes has become a graffiti gallery.

Rippling sand dunes frozen in the Arizona rock.

An isolated dive site teeming with cnidarians.

An emerald-green grotto just a short trip from Austin.

An annual festival celebrating Colorado's most famous frozen corpse.

Now abandoned, the first public health hospital in the U.S. saw more than one million immigrants from around the world.

There is nothing like a religious festival celebrated with blow-up sledgehammers.

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

The world's largest indoor go-kart racetrack is hiding in Connecticut.

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

Abandoned anti-ballistic missile base.

The remnants of an early American attempt at missile defense.

The now-abandoned tunnels were built for the transcontinental railroad on the route where the first wagon train entered California.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

This attraction was abandoned after the Chernobyl disaster.

One of the most poignant ruins of the Chernobyl nuclear disaster, the local football team's stadium has been quickly reclaimed by nature.