An early 19th-century English style garden hidden in the Rotterdam cityscape.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

One of the most easily accessible examples of the rare 1960s UFO houses.

A small square plaque marks a failed assassination attempt that could have changed history.

The unusually large seat sits atop the base of a ruined temple.

A delightful but little-known public observatory and planetarium in Munich.

Four-story slides send people whizzing through the math department at this Munich university.

In the city forest of Augsburg are oval, artificial ponds formed from a World War II bombing campaign.

Deep in the forest next to Augsburg are abandoned bunkers and bullet traps from the region's military past.

Hidden in the forest are the crumbling, graffiti-covered remains of the factory where most of Germany's explosives were produced during World War II.

The prison where Hitler wrote "Mein Kampf," and 278 Nazis were later executed for war crimes.

Hidden in the forest are the remains of a former World War II chemical plant.

The world's first jet-powered aircraft were assembled by the Germans in this secret factory in the forest during WWII.

The remains of three Luftwaffe launch pads designed for manned anti-aircraft missiles.

These abandoned Cold War-era bunkers are now a designated refuge for endangered bat species.

From Ancient Rome to WWII, Neupfarrplatz has over 2,000 years of history underneath its main square.

Massive installation of Europe's negative stereotypes.

A spiral staircase twists to the top of this unusual Czech lookout tower.

A larger-than-life statue of the German revolutionist stands proud in a small town where he never lived.

Underneath the city that invented pilsners are a series of historic tunnels that have been storing beer for centuries.

Named after the German word for "a longingness to travel," this park brings together thousands of city and street signs from around the world.

A German town is growing a building out of trees.

These paved rills bring freshwater into Altstadt and could spell wedding bells for whoever stumbles into the waters.

A geothermal energy project gone wrong is fracturing the city's picturesque architecture.