The first thermometer made with the almost-universal temperature scale is backwards.

Legend has it this spring formed at the spot where a medieval Swedish king was killed.

The final resting place of the father of modern biological taxonomy.

A hidden three-foot-wide house separates these two regal churches.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

Over time, this castle grew to encompass the entire island.

The world's largest underwater restaurant is submerged off the southern tip of Norway.

This Luxembourg cave is covered in cryptic looking marks left by mining activity.

This noble mash-up in eastern Luxembourg is part Medieval, part Renaissance, all castle.

This tri-part waterfall is a little bit of fairytale beauty in the heart of Luxembourg's Little Switzerland.

A 12th-century castle featuring a sensory path where partially-sighted visitors can experience regional history through touch and sound.

A swath of France so devastated by war it is still forbidden to go there.

This striking fort on the Maginot Line looks just as it did after being destroyed in the Fall of France.

Hiding the longest subterranean river known in the world.

An early 20th-century sanatorium, long abandoned and now being reclaimed by nature.

The highest point in Belgium is a staircase to nowhere.

Once the local rulers had gone these enchanting ruins housed common folk in an almost real life fairy tale.

Luxembourg's first beer museum honors the Grand Duchy's contributions to the art and science of beer-production.

Now overgrown, these anti-tank barriers from World War II are sometimes called "dragon's teeth."

Most powerful transmitter in Germany only broadcasts in the French language.

A former ironworks that was the first UNESCO industrial site.

A university observatory dome painted to resemble the beloved 'Star Wars' droid.

Ancient catacombs form the foundation for this Rococo orgy of a church.

The stunning interior of this Gothic church is covered in ornate gold details.