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

A tribute shrine where the Space Invasion street art movement started.

The video game-themed street art first popped up in the French city.

Stripes of human ashes cover a back lawn in the most sought-after burial grounds in Paris.

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

The Argonaute submarine was the French navy's pride and joy in the 1950's.

A mud statue stands in the dark tunnels, seeming to hold up the weight of the city above.

The former home of France's controversial pop maestro is almost completely covered in ever-changing tributes and graffiti.

Remains of Roman amphitheater hidden in a sleepy quarter of Paris.

A lone cannonball remains lodged in the walls of the Hotel de Sens as a sober reminder of a revolution.

The narrowest street in Paris.

The curious underground history of keeping Paris clean.

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

How did a French journalist’s grave become the sexiest statue in the cemetery?

In the best of all possible worlds, everyone will get a chance to see this statue in which Voltaire's heart is interred.

An overlooked marble is the only surviving in-place 18th century example of the measurement that changed how we define distance.

A subterranean shelter remains intact under a busy Paris railway station.

Indents in the pavement are all that remain from a grisly death machine in Paris.

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

A haunting collection of the vanished and disappearing natural world.

This charming cobbled backstreet is the most Instagramable street in Paris, much to the residents' annoyance.

Abandoned railway line circling the city of Paris.

France's most famous cemetery, with some of its most curious tombs.

A former suicide bridge is now accumulating symbols of love instead of a body count.