Iceland's "Smoky Valley" is a beautiful river that is shrouded in a constant cover of steam clouds.

This eye-popping Icelandic crater lake is surrounded by red volcanic rock.

The water-powered carriages are long gone, but for over a century this funicular railway has been the fastest route to the highest point in Paris.

Historic medieval fortified city in southwest France.

A medieval church with largest and oldest collection of Renaissance frescoes in France.

The world's largest reflecting pool is just two centimeters deep.

A century-old tradition has culminated in a small but singular collection of feline effigies.

The National Railway Museum in York is the largest railway museum in the world, attracting almost 1 million visitors per year.

One of the oldest and certainly best preserved Cistercian abbeys still in existence.

Astonishing rock formations dot the Brimham Moor landscape.

A museum devoted to the science of color.

An atomic bomb-proof strongbox protects the U.S. Constitution from terrorists and thieves.

The ruins of this medieval castle in Northern Ireland have inspired artists from C.S. Lewis to Led Zeppelin.

The atmospheric road was never meant to be so creepy.

This short bridge is the only thing connecting a tiny Irish island to the mainland.

Northern Ireland's Brobdingnagian stepping stones.

Macabre astrological automaton clock dating to the late 1400s.

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

A restaurant and observation deck built in a unique broadcasting antenna.

The bunker where Hitler took his own life is hidden under this deliberately ordinary parking lot.

A fascinating insight into daily life in the Eastern Bloc.

On the Spree bank, discover one of the last reminders of a symbolic wall that divided, and was torn down by the people.

A museum dedicated to the history of a terrifying secret police is now held in their former headquarters.

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