A miniature train-ride through Slovenia's largest cave system.

The enormous 250-room Vanderbilt mansion conceals hidden doors and secret passageways.

One of the largest caves in the world open to the public.

This massive subterranean fissure is known as the "underground Grand Canyon."

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

This massive chapel in the middle of the Indonesian forest is both haunting and fowl.

An eerie, derelict amusement park in Berlin.

Double spiral staircases are not unheard of, but they are very rare.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

A massive work of modern art that appears to be a crop circle in the middle of the desert.

Built to test magnetically levitated elevators, the tower also boasts Germany's highest visitor platform.

This fantastical house shaped like a seashell brings aquatic design to architecture.

This dramatic landscape hidden on the Isle of Skye looks as though you've stepped into the magical realm.

A long spiraling walkway winds through the woods, and around a copper beech tree at the center.

A collision of human error and natural geothermal pressure created this rainbow-colored geologic wonder.

On the outskirts of a desert trading village high on the Andean plain, steel giants have been destroyed by salt winds.

Toss a Frisbee through the ruins of this Colorado gold mining town.

An ancient stone fortress considered by many to be the eighth wonder of the world.

Some of the Old West's most notorious outlaws frequented this mining town.

This beloved, centuries-old tree stands at the center of a small park dotted with archaeological artifacts.

The ruins of an abandoned church mingle with the graves at Oaxaca’s General Cemetery.

This fairy-tale castle would make Dracula (who is said to have been imprisoned there) jealous.

Eco-village hidden in the foothills of the Alps that created a massive system of psychedelic underground temples.