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

This prehistoric sinkhole lured exclusively male mammoths to their death, much to the delight of science.

Hidden in an Italian forest is a completely homemade amusement park that has taken a lifetime to create.

Mother Nature outdoes herself with this stunningly beautiful set of caves carved into marble.

A faux desert landscape in the middle of the jungle that sprouts oases during the rainy season.

A popular swimming hole that hides one of America's most deadly diving spots.

Teeming with illegal goods and services, this towering maze of vice is also a popular tourist accommodation.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

The world's highest and most dangerous infinity pool lies at the precipice of Victoria Falls.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

Northern Ireland's Brobdingnagian stepping stones.

A magically clear, blue river that seems to spring from nowhere.

A salty red wasteland in Tanzania is a breeding spot for endangered flamingos.

This expansive bridge in the Canadian wilderness was originally just built for friends.

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

A popular European tradition makes its way to the states on one of America's most famous bridges.

A sprawling nature preserve harbors the world's only living dragons.

The oldest lighthouse on America's west coast no longer needs keepers, yet they maintain the site anyhow.

An arsenic-filled pool in the Grand Canyon takes on the appearance of a giant, overflowing pumpkin.

These tombs were built into the side of a mountain so that ancient angels could reach the dead.

A tropical paradise once home to space exploration and military installations.

In which a local geological marvel becomes a quaint roadside attraction.

This corn maze so big you may want to pack a lunch, and possibly a flaregun.

Island where motor vehicles are banned -- home to the only carless highway in the United States.