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

This natural Icelandic fissure allows divers to swim right between two volatile tectonic plates.

This cemetery features modernist statues as strange as its name.

An unusual stroll through gentlemen's erotica demonstrates that pornography is timeless.

Gaze upon chocolate sculptures depicting everything from chariot races to Gaudí's famous church at this shrine to sweets.

A beautiful but toxic fountain of mercury.

Turntable anonymously received orphans, alms, and groceries.

A former steam-powered mill from the 1800s is now an industrial park with a giant steel dragon slide.

A church of bones, decorated with 40,000 human skeletons.

A gravity-defying "devil's bridge" that has a surprising architectural feature for its stability.

Retirement home for giant obsolete machines.

Descend into the tunnels to experience the life of a coal miner.

An industrial relic is now one of Europe's most staggering art spaces.

The remains of centuries of copper mining appear like an alien landscape.

The Bauhaus-style former industrial complex is considered the world's most beautiful coal mine.

A former ironworks that was the first UNESCO industrial site.

Preserved "bog person" that is over 2,000 years old.

Museum celebrating the ocean, with the largest wunderkammer dedicated to sea exploration.

A 14th century bridge built as a fortress, where the devil lurks on one of its towers.

Ancient serpentine sacrifice holder that has stood the test of time.

Natural history museum displaying a famous taxidermied St. Bernard.

A community of artists and entrepreneurs seeks a simpler life on London's waterways.

Live out your childhood construction fantasies in this one-of-a-kind gyrating hotel.

The "Prussian Versailles" that is as glorious today as when it was built.