This hulking behemoth is actually five interconnected towers built in the 1960s.

The world's first zoo for microbes collecting the horrible and wonderful things living on and around us.

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

This historic Amsterdam bar used to accept sailor's monkeys as payment.

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

A Dutch passageway's artistic, aquatic-themed makeover pays tribute to the capital city's famed waterways.

The world's only museum devoted to the wonders of fluorescence.

This gorgeous reading room houses the oldest and largest art history library in the Netherlands.

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

One of the most photographed buildings in a city known for its Modernista architecture is an abandoned squat.

The 2,000-year-old Roman columns are hidden within Barcelona's Gothic Quarter.

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

A once-secret library of Freemason history in Catalonia.

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

These molds for fiberglass statues have formed an eerie, accidental sculpture park.

A beautiful but toxic fountain of mercury.

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

Gaze upon chocolate sculptures depicting everything from chariot races to Gaudí's famous church at this shrine to sweets.

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

A stately palace has been converted into the world's largest cannabis museum.

The Boston square dedicated to the dark poet who was born nearby.

The site of one of the strangest disasters in history—a wave of deadly molasses traveling at 35 mph.

Shelves covered in dozens of coffee bean varieties fill this North End institution.

This "life-size" depiction of Mickey Mouse as a half-lobster is both whimsical and a bit creepy, standing guard over the Boston waterfront.