This gaping hole in the middle of a remote mountain lake looks like a portal to another dimension.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

A rare double mill nestled along the banks of the Aa river.

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

This disused VLF radio station is no longer in service but the surrounding town still bears its name.

Visit the ancient, mysterious Roman catacombs ... in the Netherlands.

Survival capsules find a second life as a unique hotel.

The tallest waterfall in the Netherlands is a lovely, stepped feature that is only 50 feet tall.

This miniature take on the Kremlin is one Dutch man's retirement project.

A UFO-shaped event building originally intended to be a science museum showcasing the future.

The ruins of this Dutch castle sit atop a labyrinth of once-secret tunnels and passageways, dating back over 900 years.

A grassy pyramid named after a French battle.

Birthplace of the "Cat in the Cradle" and a cluster of iconic, original windmills that let the Dutch tame the seas.

Inspired by "The Starry Night" this Dutch bike path turns into a glowing work of art each night.

A floating cat sanctuary on an Amsterdam canal.

Cat art as far as the eye can see.

A controversial art piece that harkens back to local folklore.

This abandoned viewing platform has become a monument to unnecessary government spending.

A solitary lighthouse in Spain was an inspiration to the great Jules Verne.

The ruins of an ancient Celtiberian town with incredible rock-cut buildings and a Roman aqueduct.

A breathtaking and biodiverse wilderness in the mountain setting of Ernest Hemingway's "For Whom the Bell Tolls."

This medieval fortification has weathered the centuries better than any other structure from its era.