An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

Swedish skyscraper with a 90° twist.

This chimerical bridge/tunnel appears to dead end right into the sea.

This bridge's unique architecture honors nautical heritage and encourages self-awareness.

A brutalist gem towering over the heart of Milan.

This museum tells the story of lake dwellers from 4000 BC to 850 BC, replete with stilt houses and goats.

A vast Communist-era exhibition space in the Bulgarian capital.

"Holy Wisdom" overlooks the city that became its namesake.

Sofia's legislative center is continuously reinventing itself.

A striking symbol of the Bulgarian capital.

Bridge that died in war and was resurected.

The place where World War I began.

Oriental bazaar in the heart of Sarajevo.

The first mosque in the world to receive electricity.

This historic timepiece is thought to be the only public clock in the world that keeps lunar time.

A number of craters left by fatal mortar strikes have been filled with red resin to remember those lost during the Siege of Sarajevo.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

A World War II evacuation tunnel turned into a history display of Croatian state and people.

A well-worshipped shrine to the Virgin Mary nestled inside the last of Zagreb’s historic gates.

Buenos Aires' city of the dead contains some very famous remains, including Eva Perón.

This historic, palatial theater is now one of the world’s most beautiful bookstores.

A bright little alley in La Boca is a part of tango history.

This small city park is best known for the nightly convergence of thousands of shrieking parakeets.

An ancient city hidden in the heart of the Sierra Nevada mountains.