Cryptic messages embedded in the New York City sidewalk.

New York City's smallest piece of private property.

Hidden in an ordinary Midtown building is a one-room museum dedicated to the greatest escape artist.

Named the fifth most beautiful building in America in 1885, this former courthouse boasts the best view in the Village.

A three-story copper skybridge connects two Manhattan buildings with Art Deco luxury.

The origins of midtown Manhattan's anachronistic wooden farmhouse remain a mystery.

The most confusing clock in New York.

Red frames showcase remnants of one of New York's original subway stations.

Wine bottle sculpture with a ship's stateroom inside.

A museum of magic with a Sadist past.

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

Repository for more than 22 million pickled specimens.

A clock designed to run with perfect accuracy for 10,000 years.

The final resting place to 300 Victorian-era pets hides inside the city park.

A toy store with a century-long history preserves the craftsmanship of playthings of the past.

Catacombs turned marketplace.

Kings Cross Station pays tribute to its role in Britain's best-selling book series.

A collection dedicated to the treatment of disease, held in London's oldest hospital.

Wedged between two buildings at the Great Ormond Street Hospital is this secret music installation.

The largest of London's subterranean rivers and once a mad, bad center of London life.

Dictionary Johnson’s favorite feline.

One part local history, 99 parts gruesome haunted house.

The home of aviation trailblazers, in a remote corner of the big city.

The haunting, dilapidated remains of a former poorhouse on Staten Island's Greenbelt.