Once the grandest synagogue in medieval Spain, it now stands as a memorial of the 15th-century Jewish exile.

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

This magnificent castle grew from a small Moorish fortress, and reportedly inspired two iconic Disney castles.

One of the few remaining ancient aqueducts described by Frontinus as 'the most solemn testimony of the Empire.'

The world's largest wooden structure.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

Nicknamed the "Spirit of Paul Klee," this colorful apartment building features an array of multicolored panels.

A towering monument in Spain has proven to be more labor-intensive than initially planned.

A stone slab in Madrid marks the point from which the distances of Spain's national roads are measured.

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.

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

This spooky statue sits outside a famous Prague theater.

A sculpture of the iconic East German car on four legs is a tribute to those who traveled to Prague seeking asylum.

A turn of the century building boasting some of the most beautiful art nouveau architecture in Prague.

Macabre astrological automaton clock dating to the late 1400s.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

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

Stockholm's deepest subway station is also a stunning ecological wonder.

Stockholm's decidedly unique public transit system has doubled as the world's longest art gallery for decades.

France's national museum of scientific and industrial instruments.

The water-powered carriages are long gone, but for over a century this funicular railway has been the fastest route to the highest point in Paris.