This Communist-era residential block is one of the longest residential building in Europe.

The walls and ceiling of this Polish church are decorated with thousands of skulls, with another 21,000 skeletons just below.

Naturally formed rock city in Poland.

This mysterious and once-grand memorial still embodies a remarkable architectural vision.

An underground city of salt.

Relive a Polish uprising via an enormous, century-old cyclorama.

Ruins of a late 1950s Polish ski jump ramp in the middle of the city.

Museum dedicated to "the man who moved the Earth."

A 20th-century picture show in 3-D.

The oldest wind turbine in Europe, constructed by a group of friends in 1932.

Countless stories attempt to explain Poland's mysterious J-shaped trees.

Architecturally stunning library serves as the hub of Finnish scholarly life and culture.

One of the oldest libraries in England, and one of the last of the great medieval chained collections.

A visionary precursor to the Internet made of index cards.

A serpentine highway twists and turns over the treacherous Norwegian Sea.