This huge pile of volcanic boulders hides a stunning network of secret grottoes.

A thorough look at the development and history of the underground's rolling stock of the Madrid subway system.

Designed in the Romanesque style, this structure was once a fortress monastery.

A large collection of solar and night-time telescopes dot a small area on the Teide mountain range.

This Gothic church houses ornate royal tombs and a magnificent gilded altarpiece.

The world's most elegant power lines.

The most elaborate of 12 medieval arched doorways to the old city of Burgos.

A curious memento mori hangs in the magnificent Cathedral of Segovia.

This remarkable museum sprung from one of the most important prehistoric archaeological sites in the world.

Giant topiary dog once played a role in a terrorist bomb plot.

Spain's unique Mosque-Cathedral has been a place of worship for both Muslims and Christians throughout its history.

A Spanish town built into the cliffs.

The final resting place of the great navigator, or maybe his brother.

The oldest restaurant in the world is this old-world Spanish eatery, still known for its suckling pig.

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

The ruins of a 2,000-year-old Roman fishing village perched on one of the best beaches in Spain.

The world's largest wooden structure.

One of the most spectacular bridges in Spain spans a narrow chasm that divides the city of Ronda.

A curious carving hides on a marble column in the Mosque-Cathedral of Córdoba.

Moorish signal station on a stratgic rocky outcrop.

A sculpture serving as an homage to Pope John Paul II.

The remains of this 2nd-century Roman temple are incorporated into a modern building.

An ancient Roman temple first dedicated to an emperor's wife is now a church.

The only remaining arch of the oldest stone bridge in Rome stands in the middle of the Tiber.