Rare karst landscape eroded from a flat seabed.

This fairy tale forest hides scenes from some of the more obscure and bizarre Western nursery stories.

An open-air sewer system that was covered piece-by-piece over 300 years.

Most prolific publishing house in the 1600s open to the public.

A 14th-century fortified keep showcases the masterpieces of an ingenious 20th-century clockmaker.

Striking occult iconography on a medieval German church.

Of the many chalices in the running for the Holy Grail, this one in Valencia Cathedral sure looks the part.

The world's largest wooden structure.

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

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

Three bridges and one giant canyon make up this fantastic Spanish settlement.