The half-mile long structure is so impressive, it even shows up on satellite images.

This 17th-century "unicorn" was cobbled together from the skull of a rhinoceros, the legs of a mammoth, and the horn of a narwhal.

The neon signs from Las Vegas' past find their final resting place at this unusual graveyard.

Every autumn, this hillside is ablaze with red summer cypress.

This isolated island is often capped by its own fluffy cloud.

Scattered around Atlanta are little doors with big charm.

This narrow path was cut right into a French mountainside to feed the country's early naval expansion.

An architectural oddity of six stories, accessed by graceful ramps.

The oldest and smallest cemetery in Paris is only open to the public twice a year.

A haunting collection of the vanished and disappearing natural world.

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

This massive library holds what was once the largest book collection in the world.

The oldest stone house in Paris was built by its most famous alchemist.

Abandoned railway line circling the city of Paris.

The macabre collection of Jacques Sirgent, an expert scholar on the undead and all of their trappings.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

Behind the pink curtain, Au Bonheur du Jour, an art gallery of erotic archives.

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

This museum houses an imposing skeleton army comprised of creatures great and small.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

A scandalous Art Nouveau collaboration that set Paris all atwitter at the turn of the century.

A mechanized clock where a man fights off a dragon, crab, and rooster.

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.