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

The largest preserved walking dragline excavator in Western Europe.

Fantastically decorated underground chambers built in the 1760s.

A harem-inspired Moorish fantasy design in a Victorian-era Welsh castle.

19th century museum with an eclectic mix of curiosities, from Egyptian artifacts to items on archery history to the skull of the world's oldest horse.

Detailed sandstone carvings show an array of symbolism and adorable animals.

A 200-year-old prison that now houses a peculiar crime museum.

England's oldest surviving hedge maze has been confusing visitors for over 300 years.

Amazing collection of folly buildings in Cobham, Surrey.

Rebuilt remains of a temple to Roman god Mithras.

Abstract dinosaur models in London.

Obelisks and stone pineapples in the Irish countryside.

A corkscrew-shaped barn in Ireland.

Venice's island of the dead.

Ghosts of France's colonial past.

World's only telecommunication tower with a wooden pinnacle.

A complex, nine-layer maze on the grounds of a Venetian doge's playground.

The prototype for all Nazi concentration camps.

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

A towering baroque basilica jutting out of the French countryside.

The bomb-ravaged remains of of a colossal Neptune.

This Nazi-built amphitheater was constructed on a sacred mountain site used by various German cults.

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

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.