A winding cave grotto walkway built to provide employment for veterans after World War I.

An anti-tank graveyard in the English countryside.

One of the few standing Roman lighthouses and a labyrinth of tunnels are a couple of the secrets at this historic castle.

Two beautiful Victorian-era parks replete with ornamental waterfalls and lakes.

This curious Tudor-era castle was once home to Napoleon's greatest adversary, the Duke of Wellington.

Grotto replete with mystical designs laid out in glued shell mosaics.

This forgotten chalk mine was reopened thanks to a massive effort from the local community.

This mine is home to the largest man-made hole in Europe.

A former ironworks that was the first UNESCO industrial site.

A tiny chapel clings to a precipice above Germany’s gemstone capital.

This 600-year-old home seems to defy physics.

Germany's longest suspension rope bridge.

A top-secret bunker now turned museum, is an eerie look at what life would have looked like in the event of nuclear war.

This German art chapel is perfect for those who like their worship hard, modern, and utterly alien.

This former Nazi castle was built as a school to train what would have been the future of the Third Reich.

The last bastion of Roman presence north of the Alps looms over a German town.

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

A uniquely preserved neo-Gothic church that is now home to a collection of art and woodcarvings.

This still-celebrated home was a radical architectural experiment in 3D De Stijl.

A late-medieval Dutch castle with trick fountains in its whimsical water gardens.

A long-closed church turned into a saintly skate park.

A set of beech hedges planted in the 19th century forms a tunnel that takes on a different appearance in every season.

This neighborhood of futuristic ball houses looks like an alien settlement in a science fiction film.

This World War II-era bunker hides between medieval chapels in Nijmegen's city center.