The curious underground history of keeping Paris clean.

A grotto-like lodge decorated with gilded mosaics, rocks and a noisy waterfall was the setting for the most sumptuous pleasure house of 1900s Europe.

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

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

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

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

Known as the "Dodo Manège," this carousel features a herd of animals that have disappeared—or may be gone soon.

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

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

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

Walk upon the mementos of the dead in this Parisian courtyard paved with medieval tombstones.

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

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

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

A haunting collection of the vanished and disappearing natural world.

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

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

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