Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

This cemetery features modernist statues as strange as its name.

The townhouse where the "Blood Countess" Elizabeth Báthory started her murderous career.

This museum promotes informed contraception by documenting its often secret past.

The final resting place for the remains of 143 Habsburg royalty.

The crypt of the imposing Stephensdom holds royal intestines and thousands of skeletons.

An island on the Venetian Lagoon hosts this stone chair that has nothing to do with the King of the Huns.

Thousand-year-old Viking runes adorn an ancient Greek lion at the entrance to the Venetian Arsenal.

The plague quarantine island home to the alleged "Vampire of Venice."

A gruesome combat between a hunter and a furious momma bear.

This oddly shaped boulder in Paris is rumored to be cursed.

A phantasmagoric tomb honors a Belgian artist-scientist's contributions to the world of spooky entertainment.

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

Museum on French naval history, with magnificent figureheads, a historic diving suit, and a boat used by Napoleon.

The narrowest street in Paris.

The tradition of open-air secondhand and antiquarian bookselling in Paris dates back to the Renaissance.

This frog-themed restaurant was frequented by Picasso, Saint-Exupéry, and more.

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.

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

Statue of death tucked in the University of Medicine courtyard.

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

19th century pendulum and a clock restored by a rogue group of guerilla artists.

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