Bask in the 19th century grandeur of an eccentric Freemason millionaire's private gardens.

Week-long block party becomes a competition for the best decorated street.

Mountain where Jesus was first tempted by the Devil.

Gaze upon chocolate sculptures depicting everything from chariot races to Gaudí's famous church at this shrine to sweets.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

This semi-secret storybook hedge maze is also the oldest garden in the city.

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

The curious underground history of keeping Paris clean.

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

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

A mechanized clock where a man fights off a dragon, crab, and rooster.

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

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

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

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.

The macabre collection of Jacques Sirgent, an expert scholar on the undead and all of their trappings.

The pockmarks across the building's facade are remnants of the Blitz.

The bones of two medieval royal lions were discovered at the historic fortress.

This London marker celebrates the spot where the world-famous English band was founded.

London's marvelous wildfowl reserve along the Thames.

This medieval church tower has maintained its clockworks since the 16th century.

The plunge pool is a surviving relic of a rowdy royal residence.

The London statue that imitates passersby.