This whimsical castle of grottoes was the labor of love of a French postman, and one of the greatest achievements of outsider architecture.

World War II-era Nazi compound nestled in the Santa Monica hills.

Venue for strange sideshow displays and musical acts.

A whimsical and twisted animatronic monster tour beneath the streets of Berlin.

A band of aerialists and circus performers putting on incredible shows in East Williamsburg.

A massive art collective tries a new take on Brooklyn's DIY music scene—by making it fully legal.

Check out the underground party scene at the "Burning Man of Brooklyn."

An underground mansion with fruit-bearing trees and grapes growing beneath the surface of central California.

The Wonder Road aka Doobie Lane, a mile-long strip of dirt road filled with folk art.

In the middle of an extremely unforgiving and desolate high desert is the most secret military facility in the world.

Michael Heizer's masterwork in the Nevada Basin.

A picture-perfect town, perfect for blowing up.

See massive fossils that are over 200 million years old in northeastern Arizona.

A sculpture made of 10 Cadillacs as a monument to the "Golden Age" of the American automobile.

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

A cave's rare beauty held a cavernous secret hidden underground.

A multi-storied adobe complex has been inhabited for more than a thousand years.

In the remote high desert of New Mexico, a strange array of poles beckon fury from above.

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

A museum dedicated to the alleged Roswell Incident.

"I did this all while you were watching TV."

Twice a year, visitors can tour the desolate site that birthed the Atomic Age.

These azure waters were thought to lead to the Mayan Underworld.

Every equinox this Maya pyramid puts on a spooky ancient light show.