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

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

The largest of London's subterranean rivers and once a mad, bad center of London life.

This statue of one of the engineers who created the London Underground hides a ventilation shaft for the tube lines that run under the street.

The commemorative stone column conceals a secret laboratory.

An architectural oddity hides in plain sight on this iconic London bridge.

Bronze sculpture celebrating the relationship between Churchill and Roosevelt.

Claiming to be the oldest hat store in the world, this historic haberdashery had a hand (and a head) in the creation of the Bowler.

This home on a quiet suburban street is completely covered with vibrant mosaics.

In this cobwebbed old operating theater, you can practically hear the screams of the unanesthetized patients.

The first geometric self-supporting spiral stairs in Britain are a truly beautiful sight.

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

The world's largest piece of copyrighted artwork.

In 1958, an MIT fraternity pledge laid down on this bridge and instituted a new, unique unit of measurement.

Dedicated to one of the darkest moments in Irish history.

Millions of numbers carved in glass represent the tattoos forced upon victims.

Silverware in the sidewalk outside a grocery store cements this neighborhood’s Italian culinary history.

A former waterfront market is now in the center of town due to some interesting Boston engineering.

The site where Charles Dickens gave his first public reading of "A Christmas Carol" in the US.

The site of Paul Revere's historic two lantern warning.

The American Revolution was galvanized into serious action due to the tragic clash with British soldiers that occurred at this location.

This Boston medical museum features the skull of the famous medical case of Phineas Gage.

This electronics repair store celebrates the history of computers.

This stone in Lake Geneva was once the reference point used to determine altitude in Switzerland.