A Christian monastery stands on what was once a holy Incan temple.

Built on the remains of one the Incas’ most important gathering spots, this square keeps the spirit of a fallen empire alive.

Situated on a sacred Inca site, this 16th-century cathedral took nearly 100 years to build.

This geometric feat is a testament to the Incas' mesmerizing architectural abilities.

Did Inca children also slide down these smooth rocky slopes above Cusco?

The stones of this Incan wall complex fit together so well you couldn't fit a piece of paper between some of them.

The only castle in North America to ever house European sovereigns.

Iconic red and white plaques show the creative names invented to navigate the city streets.

A little sculpture with a large wardrobe.

Go inside to really appreciate this 500-year-old technological masterpiece.

The last moments of the ill-fated Pompeiians, frozen forever in plaster.

Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

A miniature train-ride through Slovenia's largest cave system.

This is the oldest Roman-made bridge in the city still existing in its original state.

Museum celebrating the ocean, with the largest wunderkammer dedicated to sea exploration.

An early 20th-century bullring converted into a modern shopping center.

Once the grandest synagogue in medieval Spain, it now stands as a memorial of the 15th-century Jewish exile.

Spanish architects used seized Muslim gravestones to rebuild parts of the fortress.

A 16th-century Andalusian palace.

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

This magnificent castle grew from a small Moorish fortress, and reportedly inspired two iconic Disney castles.

One of the few remaining ancient aqueducts described by Frontinus as 'the most solemn testimony of the Empire.'

This sweet-toothed bear searching for snacks has been a symbol of Madrid for decades.

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