This picturesque Umbrian city has a subterranean side that has long remained hidden.

This Italian foot path winds through the mountains via 52 individual tunnels.

The astonishing collection of an infamous criminologist.

This Tuscan lake hides a 13th century town that is still visible when the water recedes.

Dramatic sea stacks adorn the coast of this small village on the Adriatic coast.

Romans built the world's tallest artificial waterfall in 271 BC.

Where Aleister Crowley taught magick in "La Chambre Des Cauchemars," his "Chamber of Nightmares."

An Italian ghost town that fought obscurity, until a mysterious illness brought it to its knees.

Long-abandoned art nouveau baths beneath Milan's Piazza Oberdan.

Crossing this suspension bridge feels like walking through the sky, a fitting tribute to the head of the Apollo program.

Medieval town turned hippie commune, once home to the secret foreskin of Jesus Christ.

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

This abandoned Brutalist treehouse is a hidden architectural relic.

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

This real life asylum of horrors is now an abandoned ruin that hides the unbreakable code to one patient's insanity.

This museum is rotten with a century of wax medical deformities.

Eco-village hidden in the foothills of the Alps that created a massive system of psychedelic underground temples.

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

A fairytale island floats in the middle of Italy's little-known Lake Orta.

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

This magical-looking island is notorious for the misfortunes suffered by its owners.

This immaculate and historic water garden culminates in a massive stone dining table with an inset fountain for chilling the wine of the Cardinal's guests.

The plague quarantine island home to the alleged "Vampire of Venice."

In Rome’s Jewish ghetto, a 200-year-old bakery still makes the neighborhood’s historic sweets.