Catacombs turned marketplace.

This series of Scottish caves has no clear purpose other than baffling historians.

Spend the night in this formerly abandoned traditional Scottish village.

The longest hedge maze in the world.

Several plaster noses are hidden in plain sight around London's Soho neighborhood.

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

A hands-off space for graffiti artists to hone and display their skills.

The curios of pharmacist and collector Henry Wellcome.

The fountain marks the area where hundreds of accused witches were burned at the stake.

Rebuilt remains of a temple to Roman god Mithras.

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 vast overgrown cemetery, once known as one of London's "Magnificent Seven."

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

Eighty million natural history specimens call this gargantuan museum home.

One part local history, 99 parts gruesome haunted house.

Northern Ireland's Brobdingnagian stepping stones.

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

The atmospheric road was never meant to be so creepy.

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

360° views of the city plus five floors of optical illusions and hands-on science.

Famously misunderstood wonder of the ancient world

The hidden "ballroom" under a mansion lake was built by a criminal who ate a cyanide pill during his trial.

A charming 17th-century alley is lined with secondhand bookstores and antiquarian shops.

A 30-acre garden inspired by the principles of modern physics.