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

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

Hiding the longest subterranean river known in the world.

Around 100,000 bodies are buried below the medieval headstones, many of which mark graves with multiple bodies stacked up to 12 deep.

Looming communist pillar with a Czech twist.

Museum in a swimming pool where the water still flows.

The celebrated eyesore created by starry-eyed sweethearts.

A Museum of Psychiatry in a still-operating mental institution.

A 14th-century fortified keep showcases the masterpieces of an ingenious 20th-century clockmaker.

A little sculpture with a large wardrobe.

Theme park featuring miniature replicas of European monuments.

Climb inside an iron crystal magnified 165 billion times its normal size.

Lavish royal estate punctuated with heated greenhouses.

A sculpture park of the tossed aside relics of the USSR, from Stalin to a massive Soviet emblem.

Moscow's imposing monument to the Space Age.

This building holds the embalmed remains of the leader of the Bolshevik Revolution.

Museum celebrating the achievements of the Soviet space program.

An abused and forgotten metropolis, abandoned for centuries.

In this historic region, homes and churches are carved into ancient volcanic rock formations.

Mausoleum and Holy Seat of Antiochus I of Commagene.

A visionary precursor to the Internet made of index cards.