A burial vault located under Tiber Island in the middle of the Italian capital.

One of the most important yet well-hidden museums dedicated to the history of medicine.

A collection of objects supposedly singed by the hands of souls in purgatory.

The skull of the patron saint of lovers lies in the Basilica di Santa Maria in Cosmedin—maybe.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

A museum dedicated to one of Paris’s most famous residents, tucked into a corner of one of the city’s most famous squares.

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

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

Behind the pink curtain, Au Bonheur du Jour, an art gallery of erotic archives.

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

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

The oldest stone house in Paris was built by its most famous alchemist.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

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

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

Superb sweets await at the first Jewish bakery inducted into Berlin’s prestigious baker’s guild.

The best bagels in Berlin are tucked away in an independent bookstore.

The site where a plot to assassinate Hitler was planned—and its conspirators were executed—is now a powerful memorial to the German resistance during World War II.

The walls of Germany's Parliament still show the scars of the Red Army takeover in World War II.

Super-heavy Nazi architectural experiment.

The bunker where Hitler took his own life is hidden under this deliberately ordinary parking lot.

This World War II bunker now survives as a documentation of the Nazi regime and war crimes.

On the Spree bank, discover one of the last reminders of a symbolic wall that divided, and was torn down by the people.

A museum dedicated to the history of a terrifying secret police is now held in their former headquarters.