The world's largest reflecting pool is just two centimeters deep.

Cliffside houses provide a spectacular view from their perch above the valley.

Bordered by forest on three sides and the ocean on the other, the Great Dune of Pilat is the highest sand dune in Europe.

This gem from the industrial age helps visitors and residents alike traverse hilly Stockholm.

It is said that each of the white stones in the red facade of this medieval house represents the head of a murdered Swedish noble.

Stockholm's decidedly unique public transit system has doubled as the world's longest art gallery for decades.

Stockholm's deepest subway station is also a stunning ecological wonder.

18th century opera in its original splendor.

This massive subterranean fissure is known as the "underground Grand Canyon."

A whimsical bridge adorned with decorative dragons.

This one-time health resort was used by aristocrats around the world.

The massive white mound and accompanying water terraces are a striking geological oddity.

Hungarian self-built castle.

Possibly the world's largest hourglass only needs to be reset every New Year's Eve.

A fake Transylvanian castle houses a cathedral of antlers.

This Hungarian castle was built out of cardboard and wood until it proved so popular that it got upgraded to stone.

This hidden art nouveau gem was designed by an architect in search of a national style.

This ancient theater was once the home of fierce gladiatorial battles.

A unique underground structure dating back to the 1st century BC.

This ancient Roman bridge and aqueduct still stands as a wonder of classical construction.

A medieval church with largest and oldest collection of Renaissance frescoes in France.

Traditional 11th-century outdoor tannery.

Mosaics, storks, and brothels—this ancient city has it all.