Spain's unique Mosque-Cathedral has been a place of worship for both Muslims and Christians throughout its history.

A curious carving hides on a marble column in the Mosque-Cathedral of Córdoba.

This former charity hospital for elderly clergy houses some of Seville’s most treasured paintings.

The final resting place of the great navigator, or maybe his brother.

The world's largest wooden structure.

One of several skulls claiming to belong to the beheaded St. John the Baptist is on display at this Roman church.

Installed in an act of one-upsmanship, the annual sundial in this church is also a symbolic victory for the Gregorian calendar.

An abandoned Byzantine fortress and notorious prison.

Roughly 17 million letters to Santa have found their way to this Arctic Circle post office.

Visiting dignitaries and Hollywood stars once stayed at this 1920s hotel, alongside ghosts that are said to haunt its corridors.

If you’ve ever seen a picture of Machu Picchu, then you’ve seen a picture of Huayna Picchu—you just didn’t realize it.

A set of ancient drawings in the desert of Peru that are so massive, many of them can only be fully seen from the sky.

The intricate stonework of Machu Picchu serves as a testament to Incan engineers.

The best place in the world to buy tinned fish.

One of the smallest bookstores on the planet.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”

The world's oldest bookshop still in operation.

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

This unreal Portuguese palace looks as though it's made from a pile of different castles.

A 16th century chapel decorated with bones, skulls, and entire bodies hanging from the wall.

A stunning 18th-century site where pilgrims ascend by a series of punishing stairs only to return via funicular.

Ancient catacombs form the foundation for this Rococo orgy of a church.

The stunning interior of this Gothic church is covered in ornate gold details.

Elaborate tile work in this railway station tells the story of Portugal.