The "Black Arch" guards the entrance to the picturesque Glens of Antrim.

A hidden art gallery in an abandoned Warsaw fort.

An unusual number plate signifies the building's saucy past.

Walk through spectacular aisles of hanging meat and wagon wheel–sized cheese at the world's largest wholesale food market.

The former home of France's controversial pop maestro is almost completely covered in ever-changing tributes and graffiti.

A pre-Hispanic pyramid in the middle of a tourist district in the Canary Islands.

The remains of a 1st-century aristocratic Roman town house featuring beautiful well-preserved mosaics.

The last four extravagant street signs of London's historic banking street.

Art Deco and “Wrenaissance” mash-up, this recently restored royal residence has been home to kings and comes with secret monkey passages included.

A friendly pub with a sordid past in cock fighting.

A mysterious pair of mice eating a piece of cheese is London's smallest public sculpture.

London's last remaining public soapbox site has seen speeches from Karl Marx, Vladmir Lenin, and George Orwell.

London's old-school healing garden.

This massive collection of British military artifacts includes the heartbreaking personal letters of the men in the trenches of WWI.

The remains of Crystal Palace Great Exhibition of 1851.

This wildly-tiled artist's palace is a living and growing account of the creator's life, loves, and labors.

A mysterious artist-run cabinet of curiosities and library.

The popularity of Sherlock Holmes led to the creation of his fictional address, turning the orderly London street numbers askew.

This palatial spiral staircase was so unusual the name "snail" was given to the noble family who built it.

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

This abandoned island off the Venetian coast has been a radical monastery, a political prison, and a secret Nazi base.

Hanging within this medieval church are the bones of a beast allegedly slain by a fourth-century saint.

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