A museum dedicated to a secret military hospital hidden beneath a castle in Budapest.

A Trabant car, a kangaroo statue, and a plethora of plants take over this abandoned-factory-turned-bar.

This Hungarian castle was built out of cardboard and wood until it proved so popular that it got upgraded to stone.

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

Built in 1870 at the bridge that connected Buda and Pest, this spectacular incline railway was almost lost forever during World War II.

A trail of iron footwear stands as a monument to the thousands executed along this riverbank during WWII.

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

Preserved portions of Athens's ancient defenses are on display in a subterranean parking garage.

A Byzantine church containing the holy remnants of three saints sits atop the site of an ancient temple.

This graffitied 19th-century building was a prototype of European industrial architecture.

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

Heralded as the world's first theater, these ruins are often overlooked as they reside in the shadows of the Acropolis.

The ruined doorway is a portal to the building's turbulent and torturous past.

Where commuters walk through remnants of an ancient Greek necropolis.

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

The ruins of an ancient Roman tomb hidden in the basement of a trendy clothing store.

The Cycladic architecture makes this Athens neighborhood feel like an island paradise hidden in the shadow of the Acropolis.

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

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

A fearsome dragon clings to a corner of Munich's city hall.

Cold war icon and onetime "hole" in the iron curtain.

This water-tower-turned-high-end-apartment building was once the site of an early Nazi concentration camp.

The world's first clock to use set theory as a measure of time required the invention of a new light bulb just to maintain its obtuse measurements.

Someone loved this song enough to carve all of its lyrics onto a tree trunk in a Berlin park.