This gallery commissioned by Cardinal Spada is known for its magnificent optical illusion.

Its interior is adorned with some of the best examples of early Christian mosaics.

This ancient trail climbs the mountain where a Latin League cult worshipped Jupiter, its main deity.

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

A magnificent waterfall is also home to the remains of a Roman hydraulic engineering system.

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

One of the most important yet well-hidden museums dedicated to the history of medicine.

Museum dedicated to literary greats of the Romantic Period is also the home in which Keats met his untimely end.

This hill made entirely of ancient Roman jars was simply a garbage dump to the people of the time.

An abandoned Roman salami factory has found new life as an art space home to 200 squatters.

The Pope’s secret escape route.

A Nesting Doll of Churches.

A collection of objects supposedly singed by the hands of souls in purgatory.

A fairy tale castle in modern Rome.

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

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

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

The underground sanctuary of a mysterious ancient cult.

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

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

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

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

In Florence's great Duomo, a 26 foot fresco honors a mercenary famous for attacking Florence.

Legend says this mysterious stone head belongs to a woman who was petrified by an alchemist.