Home of the future Emperors of Russia.

The "Mystery and Company of Merchant Adventurers" is an Elizabethan-era hangout in Moscow.

Immortal combat in a Moscow museum.

Dr. Strangelove-esque tours reveal the inside a bunker once reserved for Stalin himself.

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.

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.

This former Baroque palace on the historic Calle Montcada is a rare architectural gem and was once the meeting place of an aristocratic scholarly society.

A temple to modernity, tucked away amid Barcelona's more well known museums.

Bask in the 19th century grandeur of an eccentric Freemason millionaire's private gardens.

A once-secret library of Freemason history in Catalonia.

One of Europe's largest supercomputers is housed inside of a disused chapel.

This Funeral Hearse Museum represents the finest in cadaver transportation.

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

Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

Turntable anonymously received orphans, alms, and groceries.

Mountain where Jesus was first tempted by the Devil.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

This semi-secret storybook hedge maze is also the oldest garden in the city.

A beautiful but toxic fountain of mercury.

This cemetery features modernist statues as strange as its name.

This 1920s Amsterdam neighborhood was built as a giant experiment in concrete construction.

This unattributed sculpture in Amsterdam is hiding in plain sight.

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