The world's first invisible city square is an homage to a man who pushed the boundaries of art.

Museum deep in the catacombs of St. Michael the Archangel Church is explored by touch, sound, and smell.

This magnificent Art Deco church is a reflection of Lithuania’s turbulent history.

Ever-growing collection of devils in art.

A miniatures park with a model of Wolf's Lair as it looked during World War II.

Once frequented by heavyweights of the Russian arts scene, this café is stuck in the 1800s.

The "Prussian Versailles" that is as glorious today as when it was built.

Solar observatory doubles as a daring display of Expressionist architecture, much to Einstein's chagrin.

A unique Soviet mosaic preserved on the facade of a shoe factory in Lviv.

A painfully obvious spy house sits right across the street from the Russian Embassy.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

A treasure trove of artifacts, books, and artwork from the "golden age" of exploration.

The largest manmade caves in Europe now function as a motorbike club's headquarters.

A forgotten and crumbling Yugoslav monument to the victims of fascism.

Explore this medieval cathedral by trying to spot all the malevolent monsters hiding in its beautifully colored windows.

Only museum in the world devoted to bookbinding and book arts holds a permanent collection representing five centuries.

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.

During World War II, the Nazis repurposed this beer cellar to store stolen artwork.

To the great disappointment of doomsdayers, this codex merely contains records of the Moon and Venus.

This natural history museum houses one of the world's largest rat kings, a terrifying jumble of tangled rodents.

A remarkable cabinet of curiosities in an art space in the center of Berlin.

This obscene artwork on the side of a newspaper office pokes fun at a rival paper's former editor-in-chief.

Antique frame collection with 2,400 frames.

A unique Holocaust memorial tells the personal stories of the Jewish residents exiled from greater Berlin.