This French castle is said to have once held the Holy Grail but is now a gorgeous mountaintop ruin.

A self-built mosaic house and sculpture park.

The encased skull that is widely believed to belong to St. John the Baptist.

A mosaic-tiled house built by graveyard sweeper Raymond Isidore.

The great Italian Renaissance painter was laid to rest here in the Chapel of Saint-Hubert.

A public park off the beaten path with a beautiful waterfall and 13th century Cistercian abbey.

Hundreds of secret cabinets built into the walls of legendary poisoner's private work room.

The world's tallest bridge is also possibly the most elegant.

A natural arch carved by a river gave its name to the so-called "Cave of Forgotten Dreams."

Beautiful carved tunnels.

This professional clown's home is an outsider art wonderland.

Sleep in a climate-controlled plastic bubble for the night.

This salt marsh in Southern France is as pink as the flamingos that inhabit it.

An aluminum skeleton brings Chinese mythology to the French shore.

At Monet's beloved home you can still see the Japanese bridge, waterlilies, and weeping willows that were the subjects of some of his most iconic paintings.

This natural French spring has been turned into a magical grotto by Roman and medieval constructions.

This massive blockhead sculpture hides an entire library.

Do these monsters look familiar? The gargoyles on this church are all from pop culture.

The largest underground church in Europe.

This charming cobbled backstreet is the most Instagramable street in Paris, much to the residents' annoyance.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

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

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

This jaw-dropping 19th-century bridge uses its reflection to form what appears to be a perfect circle.