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

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

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

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

Installed in an act of one-upsmanship, the annual sundial in this church is also a symbolic victory for the Gregorian calendar.

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

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

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

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

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

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

2300-year-old Roman road connecting the empire.

The underground sanctuary of a mysterious ancient cult.

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

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

Bring your own cardboard to the slippery slopes of concrete hidden in a neighborhood park.

An artsy hidden staircase leads to breathtaking views of San Francisco.

One of the oldest of its kind.

This elaborate towering structure was once famed for its revolutionary height.

Yo, Adrian!

Huge masonic hall in Philadelphia with lavishly themed rooms.

World's first "penitentiary," meant to be humane, drove men insane.

America's most famous museum of medical oddities is home to the remains of Albert Einstein's brain.

A layered tribute to the work of mosaicist Isaiah Zagar.