These Victorian era devil sculptures were designed to spite a local vicar.

The last four extravagant street signs of London's historic banking street.

This hidden green space is the city's second largest conservatory.

A 2000-year-old Roman amphitheater lies just below Guildhall Yard.

Rebuilt remains of a temple to Roman god Mithras.

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

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

Abandoned railway line circling the city of Paris.

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

Medieval museum built over Roman baths that features famous tapestries of a lady and a unicorn.

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

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

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

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

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.

A modern-day Lascaux cave underneath Paris.

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

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

Original cabaret handbills, posters, and feline artwork are a purrfect highlight of the Museum of Montmartre.

A poem by Arthur Rimbaud is inscribed on the wall of a street that, while it is only one block long, plays a key role in multiple novels.

This mural painted by Keith Haring was done without payment as a gift to entertain the children at the Hôpital Necker.

This little-known relic crypt holds stolen parts of a Roman Empress.

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

Beggars were miraculously "cured" of their fake ailments when they returned home to this 17th century Paris slum each night.