A lavish 16th-century mansion filled with spectacular staircases, fantastic frescoes, and gorgeous gardens.

One man's quest to fix his toilet unearthed over 5,000 artifacts spanning more than 2,000 years of history.

These gutted monastery ruins still stand proudly in the middle of the Italian countryside.

"Stairs of the Turks", a chalky white cliff eroded conveniently into stairs, allowing for easy pillaging.

People have been living in the cave houses on this Italian hillside since the Neolithic era.

The sinister ruins of one of the worst dam failures of the 20th century lie in this astonishing alpine setting.

The world's most active stratovolcano is almost always erupting.

An underground paleo-Christian burial site composed of the remains of several cemeteries and Basilicas.

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

This abandoned Brutalist treehouse is a hidden architectural relic.

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

This shining multicolored metro station deep under Naples is said to be the most beautiful in Europe.

Dug as a secret royal escape route, the tunnel became a wartime bomb shelter and dumping ground for vintage cars.

The glowing blue Nymphaeum of Emperor Tiberius.

Sitting on an Italian hilltop is this surreal fortress built by the mad inventor of electrohomeopathy.

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

Architectureal fantasy quarter of Rome.

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

A breathtaking bridge that crosses a vast gorge over a river's torrents, and has a tale of a devil architect attached.

A historic observatory precariously perched at the "Top of Europe."

This amazing pedestrian suspension bridge in the Swiss Alps would give Indiana Jones nightmares.

This lovely little bridge hidden in a Switzerland gorge is essentially a fairytale.

This 170-year-old Swiss guesthouse built into the side of a mountain is best accessed by a cable car.

An abandoned textile factory on the "island of crows" was home to Estonia's first workers' strike.