This domed temple was built in a hidden cave mouth as a refuge for sinners seeking absolution.

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

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

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

On rare days, this abandoned castle's gatekeepers open its doors, revealing the eye-popping splendor hidden inside.

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

Skulls and skeletons are omnipresent in this church dedicated to souls trapped in purgatory.

A small island less than half a mile from Venice is a forbidden island with a dark and twisted past.

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

A submerged archeological park still holds the wonders of a Roman Sodom.

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

Macabre museum devoted to historical Viennese murders.

The townhouse where the "Blood Countess" Elizabeth Báthory started her murderous career.

Collection dedicated to funeral rites, equipment, and mourning rituals of the Viennese.

Op-art architecture designed for happiness.

This futuristically sylvan church is a glass-enclosed marvel of modern architecture.

This haunted hotel built on natural springs once served as a hospital for a quack doctor promising a cure for cancer.

This centuries-old wooden wonder was built in less than a year and is one of Europe's largest timber-framed churches.