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

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

The ancient tomb acts as a calendar that keeps perfect time.

Obelisks and stone pineapples in the Irish countryside.

A corkscrew-shaped barn in Ireland.

Home with Gothic windows featured in a famous painting.

A bizarre house filled with an astounding array of collections.

This cave holds a surprisingly colorful variety of geological oddities.

"World's largest scrap metal sculpture" stands in an outdoor sculpture garden in the middle of Wisconsin.

The largest self-built castle in the U.S., six decades in the making.

Home to the world's oldest functioning orrery.

“And the Lord said unto Johan, build for thee an ark for the end of the world is approaching.”

Live a night as a Byzantine King, with a minibar and private jacuzzi.

A sacred lake with thousands of sacred carp and a biblical history.

Collapsing castle on the Hudson river was once the storage site of military surplus business.

A 56-foot tall statue of the god of fire looks out over Birmingham, Alabama.

Robots, lasers, and whoopee cushions, oh my!

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

In this historic region, homes and churches are carved into ancient volcanic rock formations.

This "floating island" plateau sits 7,671 feet above the forest floor.

Mysterious Spanish catacombs of unknown origins.

This rocky spread has been squeezed up directly from the bowels of the earth.

"Dark Sky Park" is heaven on Earth for astronomers, one of the rare U.S. locations with no artificial light pollution.

Cretean quarry suggests real-life site for ancient Greek myth of the man-eating Minotaur in his labyrinth.