A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

Fall down the rabbit hole into a surreal journey of human consciousness "from ass to soul."

A whimsical and twisted animatronic monster tour beneath the streets of Berlin.

An eerie, derelict amusement park in Berlin.

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

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

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

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.

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

Week-long block party becomes a competition for the best decorated street.

Mountain where Jesus was first tempted by the Devil.

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

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

The former home of a mad diplomat is said to still be marked in bloody, arcane scrawls.

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

A working miniature city designed to teach kids about safety and presumably city planning.

An eccentric home stands out in an otherwise average neighborhood with mosaics, mini topiaries, and kinetic sculpture.

This amazing pedestrian suspension bridge in the Swiss Alps would give Indiana Jones nightmares.

A breathtaking bridge that crosses a vast gorge over a river's torrents, and has a tale of a devil architect attached.

The world's longest and deepest train tunnel.

This lovely ancestral home inspired the author D.H. Lawrence, and features a tunnel made out of a living willow.

Where America's first doomsday cult awaited the end of the world.

A quirky house created entirely out of glass bottles combines a collector's spirit with an artist's flair.

One man's ambition created this psychedelic log home.