The mysterious, fantastical woodland inspiration for "The Lord of the Rings."

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

The sign at the garden gate reads: "These Plants Can Kill."

The industrial architecture honors the laborers who brought the Exposition Universelle of 1900 to life.

What looks like a normal building is really a hollow facade hiding a subway vent.

A simple plaque on the facade is the only reminder that the treaty ending the American Revolution was signed inside.

Limestone grottoes turns everyday objects into stone.

France's high-tech, future-themed amusement park.

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

A sanctuary for wolves in a community which once trembled in fear of the murderous "Beast of Gévaudan."

A unique underground structure dating back to the 1st century BC.

This submersible road connecting a French island to the mainland is lined with safety towers for when the tide strands travelers.

Statue of a decomposing prince that once held his heart in its hand.

One of the world's most complex timepieces.

A centuries-old complex of hand-dug stone chambers has sheltered locals in times of trouble.

Bits of architecture from a town destroyed in World War I now decorate this hotel garden.

A 16th-century fountain marks the site of a lost medieval cemetery once filled with mass graves.

There has been an astronomical clock on this spot since the 14th century.

Museum in a swimming pool where the water still flows.

This ancient Roman bridge and aqueduct still stands as a wonder of classical construction.

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

135 bronze medallions mark a French meridian line which once rivaled the hotshot Greenwich timeline.

Twelve grave-faced marble angels guard the emperor's tomb at Les Invalides.

A well-preserved medieval village nested on a rocky outcrop and surrounded by a network of cliffs, natural bridges and canyons.