This 47-story "M" needed 20 years to be completed

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

Spanish architects used seized Muslim gravestones to rebuild parts of the fortress.

An eerie collection of the surviving structures from a past celebration of the future.

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

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

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

This amazing example of Valencian Art Nouveau looks more like a cathedral than a public market.

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

The world's largest wooden structure.

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

This historic covered bridge contains a series of macabre paintings that communicate one thing: everyone dies.

A spectacular Petrine Baroque summer palace commissioned for Catherine I by Peter the Great.

Learn the fine art of making a centuries-old treat at this hands-on food museum.

Thousands of tourists and residents in Cologne affix "love padlocks" on the Hohenzollernbrücke Bridge to symbolize their affections.

One man's remarkable private collection of art from around the world.

This once-forgotten oasis in the middle of Lisbon was first created over a century ago quite by accident.

Portugal's National Pantheon has a history of curses, collapses and financial problems.

At night, bats patrol this magnificent 18th-century space in search of book-eating pests.

"Portugal's Stonehenge" is made up of nut-like stones aligned with the heavens.

The corpse bride of Portugal.

Located in the thermoelectric factory that once powered the entire city, this Portuguese museum is shockingly fascinating.

Elaborately carved to showcase the glorious wealth that the age of exploration brought to the Portuguese empire.

The medieval castle built as headquarters for the Pope's secretive Knights Templar.