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

A special shop catering to the needs of things that go bump in the night, and also helps kids become writers.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

Museum celebrating the ocean, with the largest wunderkammer dedicated to sea exploration.

The celebrated eyesore created by starry-eyed sweethearts.

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

This bridge was constructed from the rubble of the infamous Bastille.

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

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

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

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

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

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

Stockholm's narrowest alley is barely over two feet wide.

A former suicide bridge is now accumulating symbols of love instead of a body count.

It is said that each of the white stones in the red facade of this medieval house represents the head of a murdered Swedish noble.

Sweden's "good old days" painstakingly re-created in a model village.

The library's graceful rotunda is like a bibliophile's temple.

When this 18th-century observatory's meridian was moved, it set Sweden's time back by 0.04 seconds.

This Stockholm light tower can be controlled by anyone with a smartphone.

The site of a concentration camp where inmates were made to take part in one of the largest counterfeiting operations in history is now hauntingly empty.

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

One of downtown Berlin's last reminders of its Communist past.

The site of the famous Nazi book burning campaign of 1933 remembers its "Night of Shame".