Bridge that died in war and was resurected.

These historic defenses ensured the city within would survive hundreds of years of occupations, sieges, and invasions.

Vienna's giant wonder wheel had a starring role in one of the greatest noir movies of all time.

Baroque celebration of the end of the Great Plague of Vienna.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

This 47-story "M" needed 20 years to be completed

This imposing Masonic temple a mile from the White House was the first public library in Washington, D.C.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

A wunderkammer of gold and silver reliquaries and ancient saintly bones.

The complex has been abandoned since the Croatian War of Independence, barring a stint as a set for 'Game of Thrones.'

Gargoyle head that brings good luck.

Large, airy hallways hide within an impenetrable fortress that beckons urban explorers.

A musical instrument played by the sea.

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

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

France's most famous cemetery, with some of its most curious tombs.

The opulent home that inspired Tintin's Marlinspike Hall and the adventures within.

The "Little Ones," show Portugal in full miniature splendor.

A hidden three-foot-wide house separates these two regal churches.

"Portugal's Stonehenge" is made up of nut-like stones aligned with the heavens.

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

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

The corpse bride of Portugal.