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

This private skyway is filled with art and was expanded explicitly so that Hitler could appreciate a river.

A sinister pyramid in the Frari contains the heart of the famous neoclassical sculptor.

Pilgrimage site for star-crossed lovers.

Go inside to really appreciate this 500-year-old technological masterpiece.

This palatial spiral staircase was so unusual the name "snail" was given to the noble family who built it.

Jesus' footprints and the first catacombs in the world.

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

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

2300-year-old Roman road connecting the empire.

The final resting place of the poets Shelley and Keats.

This beautiful park on the outskirts of Rome protects the ruins of two colossal ancient aqueducts.

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

This hidden Art Nouveau courtyard is an opulent feast for the eyes.

This Venice bookstore has resigned itself to constant flooding by keeping its books in bathtubs and boats.

A two thousand year old brothel uncovered in Northern Greece.

A minotaur, a labyrinth, and a dubious restoration pull in visitors from around the world.

This ancient hydrological marvel is now the base of a modern outdoor cinema.

The railway carts travelers to central Athens's highest peak, which offers stunning vistas of the city.

A sharp sculpture made of thousands of pieces of jagged glass.

The oldest standing Byzantine church in Athens is tucked within a monastery in the middle of an upscale shopping district.

This once architecturally advanced housing complex is now a haven for squatters that still bears the scars of war.

An important example of architectural history slowly decays in the city center.

A Byzantine church containing the holy remnants of three saints sits atop the site of an ancient temple.