A natural arch carved by a river gave its name to the so-called "Cave of Forgotten Dreams."

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

This permanent collection of preserved bodies taken from Irish bogs is one of the leading authorities on such morbid mummies.

More than 5,000 artifacts donated by the people of the city, plus a room entirely devoted to the band U2.

This extinct volcano rises above Edinburgh and is special for its panoramic views over the city.

This 17th-century street hidden beneath Edinburgh was once a breeding ground for the black death.

A labyrinthine network of chambers with a storied past hides below Edinburgh's South Bridge.

Hidden in a secluded Greek cove is a pristine beach marred only by the rusting smuggler's hulk stranded on its shores.

According to the Guanches, the aboriginal people of the Canary Islands, the king of evil lives inside this volcano.

This small bronze pyramid marks the center of Belgrade, but some say it is a Masonic symbol.

Historic fortifications form the boundary of Vatican City, but it’s not entirely surrounded by walls.

This Neapolitan exhibition hall grants weird and wonderful insight into the intricacies of human biology.

Every day is like Christmas on this street where the traditional Neapolitan nativity scene comes to life.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

A large grotto built in the 16th century amidst Florence's famous Boboli gardens.

Five candy-colored villages on the Italian Riviera.

Depending on how it is measured, this lighthouse can claim to be the tallest in Europe and the tallest conventional lighthouse in the world.

The mummified relic of St. Catherine sits forever on a golden throne.

In the world's oldest university is a stunning 17th century anatomical theater carved from spruce.

Legend has it this fountain built to symbolize the Pope’s power hides a strange secret concerning Neptune's manliness.

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

Giant topiary dog once played a role in a terrorist bomb plot.

This macabre masterpiece of a mural is one of Francisco Goya's "Black Paintings."