A top secret Cold War bunker hidden beneath a Latvian spa facility is now open for tours.

Medical museum that houses most notably the taxidermied remains of Vladimir Demikhov's famous two-headed dog experiment.

A former Latvian headquarters of the brutal KGB secret police is now open as a grim reminder of their atrocities.

Flamboyant architecture from the turn of 20th century.

This abandoned secret city is a crumbling wonderland of Soviet ruins.

A former steam-powered mill from the 1800s is now an industrial park with a giant steel dragon slide.

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

This Funeral Hearse Museum represents the finest in cadaver transportation.

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

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

Mountain where Jesus was first tempted by the Devil.

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

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

This cemetery features modernist statues as strange as its name.

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

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

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

A beautiful but toxic fountain of mercury.

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

The secular incarnation of a religious meditation.

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

If you want to talk to the Pope you will have to stare down this surreal vision of Jesus rising from a nuclear hell.

The Vatican's secret porn-festooned bathroom was painted in erotic murals by one of the greatest artists of the Renaissance.

A collection of objects supposedly singed by the hands of souls in purgatory.