This hydrochronometer was invented by a Dominican monk and is a prime feature in this garden.

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

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

The spot where the fascist dictator made some of his most famous speeches including declaring war on Britain and France.

This large, circular tomb is the final resting place of the first emperor of Rome.

The Pope’s secret escape route.

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

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

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

The final resting place of the poets Shelley and Keats.

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

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

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

A rather vulgar example of the transition from Latin to the Italian vernacular.

This one-of-a-kind Roman arch is not actually dedicated to the god Janus.

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

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

Brass cobblestones mark the places where individual Holocaust victims were taken from their homes.

This Roman arch marks the location of an ancient gate at one of the Seven Hills of Rome.

A Nesting Doll of Churches.

The underground sanctuary of a mysterious ancient cult.

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

An astonishingly accurate water clock that doubles as an hourly spectacle in this Berlin shopping area.

This futuristic German television spire is actually the world's largest digital clock.