One of the only spherical 19th century gas containers left today.

The abandoned mine where American troops discovered a treasure trove of art and artifacts hidden by the Nazis.

Healing waters from a holy well, previously used by locals for doing laundry.

These 4,444 wooden steps straight up a mountain were built to serve a hydroelectric power station but these days, they're mostly used by hikers.

This early pioneer landmark is one of the oldest buildings in this part of Kansas and one of the few Dutch mills ever built in the state.

Long abandoned underground complex to keep royals safe from a nuclear war that never came.

The largest collection of the iconic wooden shoe in the world.

Remarkably preserved body discovered in a peat bog.

For centuries, this town's hot springs have been embraced by rich and poor—and even by Popes.

The only fully-realized skyscraper built by the famed American architect, Frank Lloyd Wright.

This small-town museum is dedicated to the original western movie mega-star.

One of the best examples of Art Deco architecture in the United States.

Most powerful transmitter in Germany only broadcasts in the French language.

This unique Renaissance castle was turned into a home for Nazi occultism.

A decomissioned facility where the German "Transrapid" maglev trains were once tested.

This Cold War–era fallout shelter was actually a storage facility for the nation's emergency currency.

A top-secret bunker now turned museum, is an eerie look at what life would have looked like in the event of nuclear war.

The private train station King Leopold II built for the Belgian royal family now lies abandoned.

An early 20th-century sanatorium, long abandoned and now being reclaimed by nature.

This abandoned Belgian fortress is purposefully being left to nature.

Abandoned since 1998, this train station has become an oasis for urban explorers.

One of the few standing Roman lighthouses and a labyrinth of tunnels are a couple of the secrets at this historic castle.

These 17th-century mummies are no longer naturally preserved, but remain on display today.

The vast, legendary catacombs hold secrets much stranger than stacked bones.