This city square is home to Amsterdam's oldest church and a statue honoring Dutch sex workers.

This 22-floor tower's Skydeck offers panoramic views of Amsterdam.

The attic of a four-century-old canal house hides a clandestine church.

Established in 1638 to battle the Black Death, Hortus Botanicus Amsterdam is a treasure trove of rare flora.

A floating cat sanctuary on an Amsterdam canal.

The world's first zoo for microbes collecting the horrible and wonderful things living on and around us.

A seven-century-old jail tells a not-so-pleasant history of crime and punishment.

This quaint Italian town keeps losing ground as the sides of its plateau slowly erode.

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

One of Catholicism's four major basilicas has a series of papal portraits that are said to predict the end of the world.

An enigmatic modern marker left next to a historic Roman site.

The studio built by fascists in the hopes of "reviving the film industry" with the occasional propaganda film opportunity thrown in.

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

This delightful little museum is dedicated to only one thing: pasta.

More sculpture than building, this architecturally significant temple was built on the spot of Saint Peter's crucifixion.

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

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

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

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

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

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

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

A Nesting Doll of Churches.

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