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

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

A once-secret library of Freemason history in Catalonia.

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

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

These 2000 year old remains of a Roman aqueduct are hidden inside a hotel lobby.

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

Despite attempts by local police to discourage it, Beatles-inspired graffiti has been a means for artists to air grievances for decades.

This automated sculpture of two men peeing will spell out text messages with their micturition.

An eerie, existential museum dedicated to the author of "The Metamorphosis."

Around 100,000 bodies are buried below the medieval headstones, many of which mark graves with multiple bodies stacked up to 12 deep.

Synagogue built from the stones of Solomon's temple contains the golem of Prague.

The slender brass strip in Prague's Old Town Square was used to tell time from 1652 to 1918.

Macabre astrological automaton clock dating to the late 1400s.

One of the famous Czech artist's lesser-known Prague installations appears to be a glowing fetus affixed to a drainpipe.

What looks like a suicide in progress is actually a statue of Sigmund Freud.

Bullet holes in the church wall are a reminder of the violence that followed the assassination of a high-ranking Nazi officer.

A collection of anatomical samples from one of the first anthropologists to suggest that humans reached North America by crossing the Bering Strait.

A Byzantine church containing the holy remnants of three saints sits atop the site of an ancient temple.

The oldest standing Byzantine church in Athens is tucked within a monastery in the middle of an upscale shopping district.

A Byzantine-era church hidden in a wooded area below the Acropolis.

This small, ancient Roman temple was once a church dedicated to the patron saint of penitents.

This park on the outskirts of Rome boasts two ancient Roman aqueducts and a medieval tower.

The first Russian Orthodox church in the Catholic city of Rome in almost a thousand years.