Once an opulent Art Nouveau hotspot, the Constanța Casino is one of Romania's most beautiful abandoned buildings.

The geographical center of Budapest is marked with a 10-foot-tall stylized zero.

From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

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

This small 16th-century church in Athens is almost entirely surrounded by a modern building.

The oldest cemetery of modern-day Athens blends the modern and ancient worlds.

The railway carts travelers to central Athens's highest peak, which offers stunning vistas of the city.

An ancient octagonal weather station named for the eight Greek gods of wind.

The ruins of an abandoned medieval city where the last Byzantine emperor was crowned.

Where commuters walk through remnants of an ancient Greek necropolis.

Large collection from the 3rd millennium BCE.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

150 or so scrounged-up lamps, chandeliers, and lanterns light up this alley in central Athens.

This legendary city has been a tourist attraction for centuries.

The hallucinogenic center of the ancient world.

Thousands of biblical and pagan images are carved into this small 12th-century church.

300-year-old villagers houses and traditional churches preserve a nearly lost piece of Russian history.

Gargantuan home of Russian science.

The tallest hotel in Europe.

World's largest bell sits on the grounds of the Kremlin in Moscow.

Former headquarters of the KGB.

Moscow's most popular cemetery includes the graves of numerous cosmonauts.

The gorgeous entrances into the city's underbelly look more like grand halls than subway stops.

Museum celebrating the achievements of the Soviet space program.