Stripes of human ashes cover a back lawn in the most sought-after burial grounds in Paris.

The narrowest street in Paris.

The headless bodies of more than 1,300 guillotined victims of the Reign of Terror are buried here in mass graves.

The recovered bones of martyrs slaughtered during The Terror are on display in this church crypt.

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

Natural history museum celebrating biodiversity with a parade of taxidermy animals.

In the best of all possible worlds, everyone will get a chance to see this statue in which Voltaire's heart is interred.

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

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

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

A haunting collection of the vanished and disappearing natural world.

The very center of Paris is surrounded by a bevy of strange good luck rituals.

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

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

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

Paris' linguistic guide to the international language of, yes, love.

The 2,000-year-old beam is tucked within the pedestrian entrance to the old London Bridge.

The grounds of this Jacobean estate contain one of the oldest mulberry trees in England.

Black cat statues guard this temple-like Egyptian revival factory.

The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

The broken skateboards that became a poignant memorial to a murdered skater.

Six ravens are kept captive (but well-fed) at the Tower of London to prevent the fall of the Crown.

19th-century scientists would make the pilgrimage here to verify the precision of their measuring sticks.

The remains of an ancient Roman teenager are memorialized at the base of a modern London landmark.