Amsterdam's former hotspot for public executions and dissections.

An ancient passage filled with stalls selling used books, once frequented by Vincent Van Gogh.

The narrowest house in America is seven feet of pure spite.

An early 20th-century bullring converted into a modern shopping center.

The former 1920s mansion of a prominent Catalan developer was used as the Soviet Embassy during the Spanish Civil War, and there is still a bunker below the garden.

The iconic boulevard is the perfect place to catch sight of a bicycling skeleton, a levitating Satan, or a chef with his head stuck in a pizza.

Possibly the oldest church in Barcelona, this basilica has its pagan and Christian mythologies all mixed up.

The studio of Catalonia's most famous theatrical designer remains exactly as he left it.

The largest Art Nouveau complex in the world is a Barcelona hospital with a 600-year-long history.

Mountain where Jesus was first tempted by the Devil.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

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

18th century anatomical amphitheater of the Royal College of Surgery of Barcelona.

This unattributed sculpture in Amsterdam is hiding in plain sight.

An Amsterdam street lined with antique shops each one dedicated to a different obscure collection.

The attic of a four-century-old canal house hides a clandestine church.

A beautifully eclectic mix of architectural styles.

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

Established in 1638 to battle the Black Death, Hortus Botanicus Amsterdam is a treasure trove of rare flora.

The birthplace of an eccentric alchemist and possible inspiration for the fictional reanimator of monsters.

Ruined 11th century abbey built by King David I in Edinburgh, Scotland.

Gladiators battle and chariots race daily in the ruins of a once-great Roman city.

One of nature's most well-scheduled phenomenons resides in Wyoming's Yellowstone National Park.

A gleaming white tower in ornate Indian style soars above the low-slung bungalows of north Tampa.