An ancient monastery, a locked room, and a mysterious book heist.

One man's stunning attempt at eco-friendly living.

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

This off-limits room in the National Library of France is home to a system of pneumatic tubes, once used to bring books to readers.

This Paris art space celebrates the creativity and ingenuity that springs from abject poverty, especially in Africa.

A modern-day Lascaux cave underneath Paris.

A font of vintage porn on the silver screen.

The first green space constructed on an elevated viaduct.

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

The ruins of a Duke's bucolic dream, where camels once roamed alongside "Dutch" windmills and faux-Italian vineyards.

A favorite Paris bar for U.S. expats, including Gershwin, Hemingway, and James Bond.

Egyptian Revival movie palace abandoned for decades and restored in 2013.

A Parisian cemetery where the elite and artistic are interred beneath an eccentric collection of tombs.

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

A counter-culture bookstore like no other hides in plain sight in the streets of Paris.

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

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

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

A museum of carnival attractions where you are invited to ride the rides.

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

Down a cobblestone alleyway is a museum dedicated to Romanticism, with a secret garden.

Dedicated to the history and culture of smoking, this small museum now includes a vape lounge.

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

Abandoned railway line circling the city of Paris.