This abandoned but well-preserved Prussian fortress sits abandoned in a Polish forest near the German border.

Where the interconnection of German power grids should be.

This public park collects signposts and other memorabilia related to local history, Polish-German relations and human progress

One of only two places in the world where two rivers cross each other without the waters mixing.

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

A mysterious structure left behind on the Polish mountainside, sometimes called "Hitler's Stonehenge".

The tallest stone dam in Poland was opened by Kaiser Wilhelm II himself.

This line of 12 tower mills described in the story of Don Quixote is among the most iconic landscapes in Spain.

Tallest - but not most powerful - wind turbine in the world.

Gliwice Radio Tower, likely the tallest wooden structure in the world.

This viaduct serves as a reminder of World War II.

One of Belgium's oldest hospitals saw patients from the 13th to 20th centuries before becoming a museum.

This "social palace" housing complex created a relatively stable and self-contained worker's society... for a time.

Perhaps the most beautiful of preserved saints, with a little help from Paris.

A cave dwelling that was started by the Celts, expanded by monks, and finished by knights.

This modern French ossuary contains the jumbled bones of 130,000 WWI soldiers.

The remains of 40,000 humans, meticulously stacked in a tiny churchyard shed.

The world's tallest bridge is also possibly the most elegant.

A well-preserved medieval village nested on a rocky outcrop and surrounded by a network of cliffs, natural bridges and canyons.

A centuries-old quest to create artificial life is alive and well in the French town of Limoux.

For a few short weeks in spring, this hiking path becomes a daffodil paradise.

A neighborhood church's unusual abstract stained glass was the final project of avant-garde artist Jean Cocteau.

A colossal sculptural lion built by the same man who designed the Statue of Liberty.

Today this former Nazi concentration camp stands as a poignant memorial to the victims of fascism, and a warning from history.