During prohibition, corrupt city officials ran drinking dens under the streets of Downtown Los Angeles.

This Polish cave has housed a dragon, a brothel, and an enduring legend.

Real bones which are said to have belonged to a Polish dragon.

Beneath Kraków Old Town's main square lies a hologram-filled medieval market vampire graveyard wonderland.

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

A series of abstract, silly sculptures represent the works of a great modern classical composer.

The floorboard scrawling of a tragic madman is on public display outside a Paris hospital, much to the dismay of its opponents.

A 16th-century fountain marks the site of a lost medieval cemetery once filled with mass graves.

Ghosts of France's colonial past.

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

This museum in a Paris apartment gives a unique look at the iconic French singer's life.

The famous winding walk at Chartres is surrounded in mystery and myth.

The mental institution where Van Gogh created some of his most famous work now allows guests to walk in the artist's footsteps.

The largest underground church in Europe.

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

Where the high court feasted, frolicked, and high courtesans put their royal lovers' diamonds to the test.

Noirish green neon marks the location of one of the oldest private detective agencies in France.

At Monet's beloved home you can still see the Japanese bridge, waterlilies, and weeping willows that were the subjects of some of his most iconic paintings.

Science fiction's grandfather has a fittingly marvelous tomb.

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

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

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.

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

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