The sunlight passing through the opening of this huge cave system creates a magical effect.

An abandoned quarry hides an open-air gallery of huge sculptures, some made from the rubble of 9/11.

People have been living in the cave houses on this Italian hillside since the Neolithic era.

Skulls and skeletons are omnipresent in this church dedicated to souls trapped in purgatory.

Southern Italy's spinning top village.

Geometry and mystery come together in an epic show of octagonal masonry.

A dead saint, a deadly poison, and a mysterious holy ooze.

The atomic museum in the basement of this German castle displays long strands of replica uranium cubes.

A Black Forest cuckoo clock theme park features one timepiece big enough to walk inside.

Built to test magnetically levitated elevators, the tower also boasts Germany's highest visitor platform.

The great Danube river starts here.

The narrowest street in the world is in danger of closing up entirely.

This 42-foot tribute to the workforce still reminds us to pause and recharge.

Largest illuminated advertisement sign in the world.

World's largest barrel containing an inn.

Madrid's romantically ornate crystal palace has been offering shelter to plants and art for over a century.

A whimsical brother of the nearby Fallen Angel statue takes the falling part quite literally.

A tunnel commissioned by ‘the Intruder King’ to escape from the palace if there were problems.

A medieval castle-turned-luxury villa is now open to the public.

A stone slab in Madrid marks the point from which the distances of Spain's national roads are measured.

In this 400-year-old hotel in Madrid, you'll find a comb in every room, an old clock, and maybe a ghost.

An ancient Egyptian temple in the middle of Madrid, Spain.

The oldest restaurant in the world is this old-world Spanish eatery, still known for its suckling pig.

This historic fountain is a favorite neighborhood meeting point.