A 19th century artistocrat's mansion, turned into a library, hidden in a modern library.

Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

Medieval town turned hippie commune, once home to the secret foreskin of Jesus Christ.

An alchemist's "magic door" stands in the middle of a Roman park.

Pompeii's less famous neighbor is still revealing her secrets.

This uninhabited volcanic island is the most remote in the world.

This secret coastal village is studded with pastel-colored houses all piled on top of one another.

In the middle of downtown Brooklyn lies a 165 year old secret hidden right below the surface (closed to the public indefinitely).

Remnants of a storybook amusement park hidden behind a strip mall.

Coastal dunes, site of buried Egyptian movie set and former utopian colony.

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

Home to the "Circus" trees created by Axel Erlandson.

Secret US military film studio in the Hollywood Hills.

The ghostly remains of an accidental sea.

From pre-war whiskey cocktails to prohibition-era speakeasy secrecy, this bar has seen it all.

A modern day curiosity cabinet.

Contemporary art inspired by natural history and science drawing on ancient techniques in a modern world.

World's largest collection of serial killer artwork and other macabre exhibits.

Resting place of Hollywood's immortals is also site of summer film screenings.

Small museum packed with artifacts recovered by the man rumored to be the real-life inspiration for Indiana Jones.

Most famous work of one of Frank Lloyd Wright's sons.

Panorama exhibition hall in old silent theater with a beautiful backyard garden.

During prohibition, corrupt city officials ran drinking dens under the streets of Downtown Los Angeles.