A meteorite-bounded town in Bavaria.

Hundreds of hidden passageways weave through the old quarters of Lyon.

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

The mummified heart of Louis XVII, the lost dauphin of the French Revolution.

The largest medical and anatomical collection in France lies hidden from the public.

"In the Dark" Restaurant in Paris offers dinner in complete darkness.

Abandoned railway line circling the city of Paris.

The Sun King's military models, saved from the Louvre.

Paris' fabled purveyor of exotic taxidermy and natural history curios.

This French ghost town from World War II has been left as a memorial to German atrocities during World War II.

A Belgian self-built tower inspired by the Bible and ancient civilizations.

Climb inside an iron crystal magnified 165 billion times its normal size.

Hiding the longest subterranean river known in the world.

A visionary precursor to the Internet made of index cards.

The largest ice cave in the world is thought to be the entrance to hell according to Austrian legend.

Trick water gardens from 1619 featuring a 200 piece mechanical theater powered by water.

The world's most important buildings shrunk to a tiny size.

Artfully arranged bones of 5,800 Austrians.

Ruined castle with subterranean vaulted Goblin Ha' or "Goblin Hall."

Museum devoted to the artificial language of Esperanto.

A 30-acre garden inspired by the principles of modern physics.

This Scottish bridge seems to compel dogs to leap to their death.

17th century streets hidden under Edinburgh were once a breeding ground for the black death.

Northern Ireland's Brobdingnagian stepping stones.