This tiny island featuring 9th-century Viking ruins is only accessible at low tide.

The sun acts as a key that only fits this giant keyhole twice a year.

An enormous alien invades Woking, England, as an homage to the H.G. Wells classic 'The War of the Worlds.'

This medieval church is the only one in the world that features all Marc Chagall stained-glass windows.

A road that winds through this natural cave is the only way to access the small, appropriately-named village of Cuevas.

Remarkably intact Roman stone fortifications have encircled this Spanish city for centuries.

This Gallo-Roman sanctuary is dedicated to Serápis, god of the underworld.

One of the world’s longest pedestrian suspension bridges.

The world's oldest bookshop still in operation.

The best place in the world to buy tinned fish.

This house's itty bitty size means no humans allowed.

Vibrant street art created with mixed media.

This multi-level, aqueduct-footbridge hybrid is one of the greatest works of the Spanish Renaissance.

These magnificently sculpted tombs represent Spain's own legendary version of "Romeo and Juliet."