The skull of the patron saint of lovers lies in the Basilica di Santa Maria in Cosmedin—maybe.

Architectureal fantasy quarter of Rome.

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

The underground sanctuary of a mysterious ancient cult.

An alchemist's "magic door" stands in the middle of a Roman park.

A volcanic old faithful, Stromboli has been erupting continuously for the last 2000 years.

Thousands of well-dressed mummies below a monastery.

Originally a leper colony, the island is now an Armenian monastery that's home to an incredible manuscript library and eclectic museum.

This curious building hides eclectic details like medieval gargoyles alongside naked angels and Art Nouveau mosaics.

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

The walls of this medieval church are covered with perfectly preserved frescos, including a pristine example of the Dance of Death.

Natural cathedral designed by Italian artist Giuliano Mauri.

This doorless 20th-century elevator doesn't stop or slow down.

The glowing blue Nymphaeum of Emperor Tiberius.

Colin Stokes "got a bit carried away" and built a castle that looks like something out of Tolkien.

The most gigantic, swoony, intimidating trio of fingers in all of antiquity.

The medieval castle built as headquarters for the Pope's secretive Knights Templar.

The walls and ceiling of this Polish church are decorated with thousands of skulls, with another 21,000 skeletons just below.

A fairytale Gothic castle steeped in Nazi treasure conspiracy theories.

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

This strange bovine gargoyle is said to have been put in as a passive aggressive form of revenge.

The fairy tale castle of the "fairy-tale king."

This whimsical castle of grottoes was the labor of love of a French postman, and one of the greatest achievements of outsider architecture.

On the Spree bank, discover one of the last reminders of a symbolic wall that divided, and was torn down by the people.