Hidden beneath a restaurant, underground tunnels tell the story of Malta’s tragic role in World War II.

This virtually windowless mass of smooth concrete is the only Catholic church in the city.

This exclusive resort has completely covered a tiny Balkan island in a 5-star warren of guest rooms.

A tiny church on a man-made island in the Adriatic.

A curious little museum dedicated to the furry feline in the cat haven that is Old Town Kotor.

The unusual sculptures are believed to be powerful political symbols.

A small memorial to a deadly night in Serbia that shook the world before it was swept under the rug.

In the hinterlands of Serbia's capital, a giant reflective mushroom houses an aeronautical history of the former Yugoslav republic.

A misnamed well, with a deep dark past.

Destroyed Serbian army headquarters sits half crumbled in a largely revitalized Belgrade.

A pair of connected skyscrapers form this symbolic gateway.

Nikola Tesla's ashes are held in a golden sphere, surrounded by his works.

This one-time health resort was used by aristocrats around the world.

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

This massive subterranean fissure is known as the "underground Grand Canyon."

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

Barça football fans might see the insignia hidden in a church window as a divine sign.

Originally used to sell brandy, the bull-shaped billboard became an iconic symbol of Spain.

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

A 16th-century Andalusian palace.

The iconic boulevard is the perfect place to catch sight of a bicycling skeleton, a levitating Satan, or a chef with his head stuck in a pizza.

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

Turntable anonymously received orphans, alms, and groceries.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.