Six ravens are kept captive (but well-fed) at the Tower of London to prevent the fall of the Crown.

Thanks to modern navigational tools we now know that the true prime meridian runs through a park next door.

Scattered throughout London are ancient remnants of the city's former bounding wall.

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

Eighty million natural history specimens call this gargantuan museum home.

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

This irregularly shaped sea fortress has defended not one but three different sovereign states.

A subterranean house of worship carved right out of the bedrock.

The design of this beautifully crafted building was inspired by Norwegian glaciers.

An artist's mausoleum with a haunting echo.

One man's exploration of the human form, including the bizarre and delightful "Man Attacked by Babies."

A monument to the three wars that led to German unification towers within a Berlin traffic circle.

Cold war icon and onetime "hole" in the iron curtain.

Berlin's old airport.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

The most visited, and possibly most controversial, museum in Germany.

The celebrated eyesore created by starry-eyed sweethearts.

This Parisian gem is one of the most incredible ethnographic museums in the world.

Abandoned railway line circling the city of Paris.

An early 20th-century bullring converted into a modern shopping center.

A vista of the city and sea from atop the little-known viewing deck on an unassuming Columbus statue.

The iconic boulevard is the perfect place to catch sight of a bicycling skeleton, a levitating Satan, or a chef with his head stuck in a pizza.

This sweet-toothed bear searching for snacks has been a symbol of Madrid for decades.

Abandoned for decades, trains still pass through the now-restored remains of one of Madrid's first metro stations.