The atmospheric road was never meant to be so creepy.

Monasteries on rock pillars, once accessible only by frayed ropes.

Heralded as the world's first theater, these ruins are often overlooked as they reside in the shadows of the Acropolis.

A medieval church built into an ancient cave.

This whimsical stacked cabin looks like something out of a children's book.

A mining town, now abandoned, was built in a canyon so narrow that the railroad ran right through the hotel lobby.

Panoramic views from the mountains over a facility built to provide tuberculosis patients with fresh mountain air.

It was an experiment to prove that glacial boulders and rocks can be used in constructions and dwelling.

The writing studio of an American adventure author, built in the style of a medieval castle.

The blowhole bursts spectacularly right next to the buildings in a medieval seaside town.

This 16th-century monastery has been turned into a surrealist architecture compound.

This picturesque Umbrian city has a subterranean side that has long remained hidden.

A labyrinthine underworld of tunnels and caverns hides beneath the city.

Wander among the abandoned ruins of this once-powerful medieval town.

This Norman castle has been the scene of assassination plots, religious persecution, and Nazi conspiracies throughout its long history.

The site of the first medieval crusade that pitted Christians against Christians.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

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

This unreal Portuguese palace looks as though it's made from a pile of different castles.

The birthplace of an eccentric alchemist and possible inspiration for the fictional reanimator of monsters.

The fairy tale castle of the "fairy-tale king."

A self-built castle made by a mysterious man.

A 140-year-old castle with underground caves hidden in San Francisco.

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