Catacombs turned marketplace.

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

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

One part local history, 99 parts gruesome haunted house.

Banksy gives themself artistic license with this piece of London street art.

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

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

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

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

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

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

A 300-year-old tea shop that brought tea to the English people, not to mention the Queen herself.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

The world's first electric battery-powered submarine.

The two massive guns that defended Cartagena Bay.

An ancient Roman theatre restored to its former glory in the Spanish city of Cartegena.

The former Nazi concentration camp stands as a museum to remember this dark chapter in European history.

Where Venice's gondolas go for a tune-up.

This Roman statue is missing a limb from when the Venetians stole it from Constantinople during the Crusades.

A sinister pyramid in the Frari contains the heart of the famous neoclassical sculptor.

Two stone columns flank the grand Venice square, but there were supposed to be three.

The only museum with its curator—and her pets—buried inside.

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

As can be expected from a centuries old church built in a canal city, the undercroft of this house of worship is beautifully flooded.