A museum dedicated to a secret military hospital hidden beneath a castle in Budapest.

Daily jousts and dancing barrel makers in Munich's mechanical clock.

This abandoned coliseum was intended to be a grand Nazi rallying ground before it was halted at the end of the war.

Swedish skyscraper with a 90° twist.

This chimerical bridge/tunnel appears to dead end right into the sea.

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

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

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

The Columbia Road Flower Market is now open every Sunday, rain or shine.

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

The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

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

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

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

The handiwork of a underdog clockmaker who solved an impossible problem for an Empire, and forever revolutionized seafaring.

19th-century scientists would make the pilgrimage here to verify the precision of their measuring sticks.

17th century streets hidden under Edinburgh were once a breeding ground for the black death.

A six-ton wedding present for the King of the Scots.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

This ancient Irish tower could easily have stood in for Rapunzel's prison.

The celebrated eyesore created by starry-eyed sweethearts.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

This ancient Roman bridge and aqueduct still stands as a wonder of classical construction.

This castle-fortress is a living example of the transition from medieval defenses to modern fortifications.