The site of a prison camp where Cypriot resistance fighters were held in the 1950s.

Today this former Nazi concentration camp stands as a poignant memorial to the victims of fascism, and a warning from history.

Hidden in the forest are the remains of a former World War II chemical plant.

A former Nazi lookout tower with a magnificent view of the Rhineland.

The birthplace of an eccentric alchemist and possible inspiration for the fictional reanimator of monsters.

An eccentric inventor's castle home with its own indoor weather system.

Friction between grains of sand cause a curious "singing" sound.

Palatial mansion estate used in films including "Flowers in the Attic" and "The Witches of Eastwick."

The legendary building that needed ghostly approval before being built.

Crypt mausoleum in cathedral's basement contains relics of third century Roman martyr, Saint Vibiana.

A cake-themed art installation tucked away in historic Chinatown.

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

This doorless 20th-century elevator doesn't stop or slow down.

The intended purpose of this unfinished Elizabethan building remains a mystery.

The preserved home of the first settler of "the most German town in Brazil."

Beautiful Victorian buildings from L.A.'s forgotten architectural past.

Once the central jail for Los Angeles, this building housed inmates like Al Capone, those arrested from the Zoot Suit and Watts Riots, and individuals imprisoned for their sexuality.

A relic of the old jail still stands in its original location.

This ancient Roman prison is decorated with an upside-down cross not as blasphemy but as saintly tribute.

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

This hidden Art Nouveau courtyard is an opulent feast for the eyes.

A forgotten "city of water" underneath the famous Trevi district.

This former Roman Catholic Church still contains the embalmed hearts and organs of 22 popes.

A wunderkammer of curious objects and intriguing art nestled within a hub of ancient Roman sites.