Tiny memorials honor individual victims of the Holocaust.

Beneath the impressive baroque cathedral that rises from the center of Berlin lies the largest collection of Prussian royals in the world.

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

Rare wooden escalators lead deep down into an otherwise staggeringly monotonous tiled tunnel.

The patron of this extravagant Art Nouveau confection insisted that nothing less than a boat should project from its facade.

A restaurant and observation deck built in a unique broadcasting antenna.

These former Nazi anti-aircraft towers offer a singular view of the north of Berlin in the summer, and a sanctuary for bats in winter.

Berlin's beloved bear is immortalized at the Museum für Naturkunde.

A monument to the man who almost killed Hitler.

One of downtown Berlin's last reminders of its Communist past.

The world's first clock to use set theory as a measure of time required the invention of a new light bulb just to maintain its obtuse measurements.

This water-tower-turned-high-end-apartment building was once the site of an early Nazi concentration camp.

What started as a tongue-in-cheek shrine is now a full-blown museum celebrating "The Hoff" and his longtime love affair with Berlin.

Gardens representing parts of Asia, Europe, and the Mid East are tucked away among the Soviet-style buildings in East Berlin.

Berlin's natural history museum houses the world's largest mounted dinosaur and the late beloved polar bear Knut.

A wunderkammer of mysterious objects and stories.

An abandoned NSA listening post on Berlin's "Devil's Mountain."

3,000 market stands in five former Zeppelin hangars.

Among the oldest structures in Madrid, these Moorish walls once guarded the medieval city of Mayrit.

This macabre masterpiece of a mural is one of Francisco Goya's "Black Paintings."

For decades, Puerta del Sol has been illuminated by a giant, guitar-wielding bottle of sherry.

This sweet-toothed bear searching for snacks has been a symbol of Madrid for decades.

This lucky bronze frog was gifted to Madrid by a casino.

A lush indoor jungle fills this bustling Madrid transportation hub.