Ever hear of the Milazzo Cage?

At the crypt of St. Mary of Eulogies and the Dead you are left alone to ponder mortality among piles of skulls.

The "Greatest Sewer" of ancient Rome is one of the oldest sewer systems in the world, and is still in use.

A hospital where antique dolls are given new life.

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

This Roman arch marks the location of an ancient gate at one of the Seven Hills of Rome.

Installed in an act of one-upsmanship, the annual sundial in this church is also a symbolic victory for the Gregorian calendar.

Architectural monsters are devouring this palace's every door and window.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

The real place where the One Ring to rule them all was forged.

Trace the history of writing at this unusual North Carolina destination.

Xul Solar was an artist of alternate worlds, inventor of languages, and dreamer of utopias.

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

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

This chest hospital with a dark, haunted past serves as a fitting set for horror films and a paradise for ghost hunters.

A collection of abandoned typographic signs from Berlin and beyond.

From toys to kettles to scientific instruments, this German museum celebrates the beauty of 20th century design.

Floating swimming pool within a moored vessel.

An eerie, derelict amusement park in Berlin.

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

A museum dedicated to the history of a terrifying secret police is now held in their former headquarters.

This futuristic German spa allows visitors to float in a pool of salt water while zoning out to underwater techno.