This centuries-old Italian chapel hangs midway down a sheer cliffside.

This medieval Italian town is a sheer (and beautiful) cliffside defense.

A labyrinth of ancient tunnels hidden below the city holds the ruins of 2,500 years of history.

The abandoned "Ghost Mansion" was left to decay in the mountains of Northern Italy.

This enchanting 600-year-old tree is so magical it inspired the beloved tale of Pinocchio.

A fairy tale castle in modern Rome.

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

The doodles of a genius line the walls of a secret room under the Medici Chapel, where they were hidden for nearly 500 years.

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.

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

Architectureal fantasy quarter of Rome.

This Venice bookstore has resigned itself to constant flooding by keeping its books in bathtubs and boats.

Large, airy hallways hide within an impenetrable fortress that beckons urban explorers.

This huge metal monument is slowly being stripped to its concrete skeleton.

The remains of a sunken military ship wreck visible through clear water.

An ethereal glowing blue ocean cave in Croatia.

This small town in the Netherlands has no roads but instead, miles of canals and over 100 bridges.

Beneath Kraków Old Town's main square lies a hologram-filled medieval market vampire graveyard wonderland.

Warsaw's fantastically preserved gasworks...almost.

A 20th-century picture show in 3-D.

"The most colorful grottoes of the world.

A sprawling Baroque park with 300-year-old hydro-pneumatic waterworks.

A gravity-defying "devil's bridge" that has a surprising architectural feature for its stability.