An ornate private entrance to the Vienna subway built specifically for the emperor.

A patriotic medieval knight in driven-nail armor raised money for widows and orphans of WWI.

Vienna's diversity-themed traffic lights were inspired by the Eurovision Song Contest.

This series of Baroque passageways in Vienna's cultural center mix old architecture with modern art.

Giant WWII fortresses that fired 8,000 rounds a minute, now home to thousands of pigeons.

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.

Op-art architecture designed for happiness.

The only subway station in the city that still makes use of gap fillers.

A commemorative plaque hides a door that leads down to the New York Public Library's underground book bunker.

A diminutive statue that was inspired by the sculptor's own daughter.

Spain's largest bullring offers a unique glimpse at architecture and history.

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

The world's largest wooden structure.

A triumphant marble and bronze fountain depicting a 15th-century Hungarian king and his hunting party.

From cartoon characters to tiny tanks, a guerilla sculptor's little bronze statues are hidden throughout the city of Budapest.

This fortress dates back to the 6th century and is also the site of a controversial abandoned restoration project.

Chelsea's soldiers were given strict orders when crossing this historic bridge.

London's creepiest cemetery was once the site of dueling magicians and mobs of stake-carrying vampire hunters.

The only ancient site that remains on the south bank of the sacred Ilissos river.

These caves secretly held national treasures during World War II.

Legend says it was constructed with the destroyed pillar of an ancient Greek Temple.

The only surviving choragic monument is a trophy awarded in 334 BC for the winning dramatic chorus.

A man's head is enshrined beneath a statue near the first building constructed for the modern Olympic Games.