Burial grounds for more than 1,000 bodies deep under the modern town of Rabat.

This prison on the Maltese island of Gozo is almost 500 years old, and they have the graffiti to prove it.

A hidden tunnel of bones in one of Malta's oldest churches.

This subterranean necropolis holds three floors of antler-dug grave caves.

Stone Age solar temple is aligned with the sun on each equinox and solstice.

Historic fortifications form the boundary of Vatican City, but it’s not entirely surrounded by walls.

These spartan apartments are provided to clergymen visiting Vatican City.

Stone memorial that's said to predict the death of the pope and the site of the Cadaver Synod.

The final resting place of the poets Shelley and Keats.

In the early Roman Empire, people deemed traitors and criminals were tossed to their deaths from this rock.

An ancient Roman temple first dedicated to an emperor's wife is now a church.

The ruins of the largest gladiatorial school in Rome are largely hidden under modern streets.

The only visible reminders of an elaborate engineering project that kept the tower from reaching the tipping point.

Golden cobblestones remember a time when this small alley was used to avoid having to give a Nazi salute.

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

Next to the Leaning Tower of Pisa is a cemetery home to ancient sarcophagi and disturbing murals.

Romans decided this 16th-century "talking statue" was so ugly, they named it after a primate.

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

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

One of several skulls claiming to belong to the beheaded St. John the Baptist is on display at this Roman church.

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

This picturesque horseshoe weir was first built in the 1600s to prevent flooding in the town of Bath.

The world's first underground farm is in a World War II bomb shelter beneath the streets of London.

One of three sites in England that house the National Collection of Arms and Armour.