The hidden "ballroom" under a mansion lake was built by a criminal who ate a cyanide pill during his trial.

A sixth-century Byzantine cistern hidden below a modern carpet store.

An Art Nouveau gem hides beneath the layers of city grime obscuring this once-magnificent building.

The post-apocalyptic remnants of a bucolic town ruined by a plane crash.

One of the last realized projects of an influential, self-taught, French Modernist architect Jacques Couëlle.

Perfume museum and library.

César Baldaccini's iconic sculpture of a 40-foot thumb stands tall in La Défense.

The only remaining collection of flayed figures made by French "madman" Honoré Fragonard.

The Cimetière des Chiens et Autres Animaux Domestiques is one of the oldest pet cemeteries in the world.

In this Parisian garden's grotesque former life as a zoo it fed exotic animals to the bourgeois and put humans on exhibit.

Abandoned railway line circling the city of Paris.

This Parisian café sticks almost exclusively to an ethos of reuse.

This Parisian gem is one of the most incredible ethnographic museums in the world.

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

Paris' linguistic guide to the international language of, yes, love.

The water-powered carriages are long gone, but for over a century this funicular railway has been the fastest route to the highest point in Paris.

This Parisian café is dedicated to great tea and the art of knitting.

This lesser-known Frank Gehry building houses a treasure trove of cinema history.

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

Once a 19th-century brasserie, this McDonald's exterior celebrates Alsatian design and the "King of Beer."

One of Jeff Koons’s largest sculptures and his first commemorative work.

BDSM, 1930s Style.

This Parisian fountain is a little bit fantasy and a little bit nightclub.

The subterranean "lake" below the Paris opera house inspired the Phantom of the Opera's lair.