A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

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

The gardens and chambers of this Moorish citadel conjure memories of the Alhambra.

This Moorish fortress has guarded Málaga from the slopes of Gibralfaro hill for nearly a thousand years.

This statue pays tribute to the iconic musician in the place where he recorded his final studio album.

This bronze boar's snout has been rubbed to a golden sheen by visitors seeking good fortune.

Relics designed to contain and conceal Yugoslavian submarines.

A tiny church on a man-made island in the Adriatic.

These historic defenses ensured the city within would survive hundreds of years of occupations, sieges, and invasions.

This volcanic plug boasts the longest recorded history of any Scottish stronghold.

Overlooking a Scottish loch, this beautifully crumbling castle once inspired a poem by William Wordsworth.

Overlooked by many, the two famous Scottish warriors guard the main gate of Edinburgh Castle.

A New York–based physician returned home to Spain to build his own elaborate monument to Christopher Columbus.

The castle that provided the setting for much of 'Monty Python and the Holy Grail' is now a pilgrimage site for fans.

Archaeologists believe this panel of petroglyphs depicting descending sheep and other figures in Glen Canyon are 3,000 to 6,000 years old.

A sharp bend in a dramatic river canyon cut through red rocks.

This historic national park is covered in the stunning ruins of red rock pueblos.

Ancient pueblos built into the base of a natural canyon wall.

A nature and cultural preserve named for its multitude of petroglyphs carved by the Northern Sinagua people.

A planet-hunting astrograph built in the 1920s to seek out the so-called "Planet X" beyond Uranus.

The final resting place of the businessman-turned-astronomer who helped discover Pluto stands near his observatory.