This hidden green space is the city's second largest conservatory.

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

The curios of pharmacist and collector Henry Wellcome.

A little slice of Japan and its aesthetics in London's Holland Park.

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

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

The quaint little store that is said to have inspired a famous Dickens novel was only given its name after the book was released.

A student driver's nightmare.

A subterranean ice warehouse that has lain hidden beneath central London for over a century is now open to the public.

This 1920s Dutch barge is now a floating bookstore.

This London pub hides a peculiar secret: a recreation of the rooms shared at 221b Baker Street by Sherlock Holmes and Dr. Watson.

Hidden beneath the streets of London is a secret subway that only carried mail.

A tongue-in-cheek arcade where the games are based on everyday life.

This shop and gallery is a modern-day cabinet of curiosities, unassumingly positioned along an urban thoroughfare.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

This 220-year-old house is a reminder of New York City's Dutch past.

A Yiddish theater turned movie house turned rock and roll landmark turned gay disco turned bank.

New York City's only preserved family home from the 19th century.

A hands-on traveling collection of the innovative devices of yesteryear.

An annual extravaganza of Broadway theater memorabilia.

A pedestrian island in the middle of world-famous Times Square emits a strange (and purposeful) humming noise.

A small peaceful park and waterfall tucked amid the urban grind of Midtown Manhattan.

There's a piece of New York City transportation history hidden in plain sight at a Manhattan subway stop.

Tucked away amidst some of the most famous addresses in the world is New York's only fraction of a street.