Stockholm's narrowest alley is barely over two feet wide.

These medieval ruins have survived since the 12th century, even providing shelter from the Nazis.

The castle where the Marquis de Sade lived out his darkest fantasies.

One of the oldest and largest castles in the world.

Amid the sprawling Defense Intelligence Agency Headquarters is one of Washington's least accessible museums.

An eclectic mix of influences rot together in harmony in this India necropolis.

Known as the leaning temple, the sacred structure has somehow developed a severe nine-degree slant.

The mysterious empty cupola behind the monumental arch points to an ancient prophecy of Delhi.

An ancient iron pillar in Delhi that seems to be rustproof.

An imperial fortress city that incorporated cultural elements from the entire Mughal empire, only to be abandoned the year it was finished.

The 953 windows undoubtedly make this the world's most beautiful screened porch.

The world's second-largest sundial, made entirely out of stone.

This stunning 15th-century royal hill fort preserves the age of chivalry in Rajasthan.

Once an indicator of social class, the color blue has come to define this city on the edge of the Thar Desert.

A former bastion of Rajput chivalry, this massive hill fort is the site of legend and tragedy.

This magical place built as an astronomical center starred as a James Bond villain's lair.

The oldest still-inhabited hill fort in India looks like a magnificent golden sandcastle.

An extraordinary "City of Caves" carved from solid stone.

This complex of vertically-excavated Buddhist, Jain, and Hindu monolithic temples in India's Maharashtra providence illustrates a spirit of tolerance characteristic of ancient India.

This city square is home to Amsterdam's oldest church and a statue honoring Dutch sex workers.

From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

The modern birthplace of Irish freedom.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.