This grisly effigy displays an early Christian martyr who was skinned alive and beheaded.

Da Vinci's equestrian statue, 500 years in the making.

The secret medieval communication system will whisk your words above the noise of the crowd.

An ossuary built in 1210 to collect bones from the Ospedale Maggiore of Milan.

This old medieval prison tower has been a site of astronomical research for more than 250 years.

Built to repay the sins of the father, this church is home to one of the most valuable works of Western art.

The world's oldest surviving anatomical theater, where "the dead are pleased to help the living."

One of the world's oldest working clocks is curiously missing the Zodiac sign of Libra.

The incorrupt tongue of the patron saint of lost things is venerated in this basilica.

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

The only museum with its curator—and her pets—buried inside.

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

A complex, nine-layer maze on the grounds of a Venetian doge's playground.

This abandoned island off the Venetian coast has been a radical monastery, a political prison, and a secret Nazi base.

Renaissance villa and gardens complete with a tormented colossus.

The graveyard is filled with beautiful funerary art and boasts breathtaking views of Florence.

The largest and most famous wax anatomical collection anywhere in the world.

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

A fortified medieval basilica on the Caelian Hill preserves extraordinary frescoes and one of Rome's most beautiful hidden cloisters.

A Nesting Doll of Churches.

St. Francesca Romana, patron saint of drivers, resides in the church she founded.

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

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

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