A curious carving hides on a marble column in the Mosque-Cathedral of Córdoba.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

Natural stone arches form a walkable "cathedral" at low tide, then disappear entirely when the water returns.

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

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

A hospital where antique dolls are given new life.

This beautiful park on the outskirts of Rome protects the ruins of two colossal ancient aqueducts.

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

Ruins of a 10th century church tucked away deep in a botanical garden.

A fairy tale castle in modern Rome.

Jesus' footprints and the first catacombs in the world.

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

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

Architectural monsters are devouring this palace's every door and window.

The last moments of the ill-fated Pompeiians, frozen forever in plaster.

The glowing blue Nymphaeum of Emperor Tiberius.

As can be expected from a centuries old church built in a canal city, the undercroft of this house of worship is beautifully flooded.

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

The oldest operating pharmacy in the world features 800-year-old recipes.

A large grotto built in the 16th century amidst Florence's famous Boboli gardens.

The underground sanctuary of a mysterious ancient cult.

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

A 16th-century horror show built in a lovely Italian garden.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."