This Luxembourg cave is covered in cryptic looking marks left by mining activity.

This collection of solar timekeepers includes the world's first digital sundial.

The castle that provided the setting for much of 'Monty Python and the Holy Grail' is now a pilgrimage site for fans.

This astronomical clock is the second oldest in England.

The oldest residential street in Europe also features an optical illusion.

In 1977, an eccentric book lover formed a micronation for book lovers.

This carved stone slab marked the grave of a local dragon slayer, who makes a killer pie.

Crouch down, stretch tall, and be sure to flail your legs to pay homage to the Monty Python classic.

Go inside a revolutionary, cage-less zoo where 70 species of monkeys roam free alongside their human visitors.

One of England's most famous churches hides a pair of little known architectural treasures.

Blitzkrieg bop your way through Berlin's Ramones Museum.

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

Potato-peeling mannequins, Inca art, and a dangling tuber mobile help trace the history of fries at this Belgian museum.

A beer pipeline runs beneath Bruges.

This building holds the embalmed remains of the leader of the Bolshevik Revolution.

A huge Soviet-era robotics factory in the outskirts of Pripyat, now long-abandoned.

This attraction was abandoned after the Chernobyl disaster.

The ghost town left by the worst nuclear disaster of all time is being taken over by nature and urban explorers.

The dining hall that nourishes workers in Chernobyl's Exclusion Zone is also open to visitors.

This derelict superstructure was a very important warning system for the Soviet military.

Peace Park and the Atomic Bomb Dome.

A plaque marks the site directly below the mid-air detonation of the atomic bomb over Hiroshima.

This ancient cave temple complex is the largest and best-preserved temple complex in Sri Lanka.

Known as the most scenic route in Sri Lanka, this train line is steeped in history and offers an unparalleled view of the country.