Ruined 11th century abbey built by King David I in Edinburgh, Scotland.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

This splendid mosaic embodies ancient Rome's fascination with the exotic allure of Egypt.

The city of Palestrina was built around this magnificent terraced sanctuary dedicated to the pagan goddess Fortuna.

Legend has it that this bronze orb, which sat atop an ancient Egyptian obelisk, once held the ashes of Julius Caesar.

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

An 18th century fountain and two columns are all that remains of Rome's forgotten river harbor.

Also known as the Square Colosseum, this building is a prime example of fascist-era rationalist architecture.

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

A treasure trove of Renaissance-era funerary art in a Roman church built on top of Nero's grave.

A huge enchanting public park just outside the ancient walls of Rome.

Rome's ancient Etruscan rival, now a park full of ruins.

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

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.

A Nesting Doll of Churches.

This ritzy Italian market is built around a statue of an unforgiven heretic who was burned for his belief in an endless universe.

Jesus' footprints and the first catacombs in the world.

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

The underground sanctuary of a mysterious ancient cult.

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

2300-year-old Roman road connecting the empire.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

The yawning maw of this pagan visage is said to bite off the hands of liars.