An ossuary built in 1210 to collect bones from the Ospedale Maggiore of Milan.

The last moments of the ill-fated Pompeiians, frozen forever in plaster.

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

The glowing blue Nymphaeum of Emperor Tiberius.

As can be expected from a centuries old church built in a canal city, the undercroft of this house of worship is beautifully flooded.

A large grotto built in the 16th century amidst Florence's famous Boboli gardens.

Thousands of well-dressed mummies below a monastery.

Geothermal waterfalls in Tuscany.

The doodles of a genius line the walls of a secret room under the Medici Chapel, where they were hidden for nearly 500 years.

According to the local folklore, the myriad colors of this lake are the result of a lovelorn wizard's blunder.

Stalactites and stalagmites in a beautifully lit cave.

Renaissance villa and gardens complete with a tormented colossus.

The underground sanctuary of a mysterious ancient cult.

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

A submerged archeological park still holds the wonders of a Roman Sodom.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

A 16th-century horror show built in a lovely Italian garden.

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

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

A crumbling bakery where forced laborers from the nearby concentration camp toiled to feed their fellow prisoners and Nazi soldiers.

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

This classic restaurant features a gorgeous mirror-clad room.

A state-of-the-art medical facility from the Imperial era is now a derelict ruin.

Along the banks of the River Rhine lies a park that seems unassuming, but beneath the surface lies a long and fascinating history.