Croatia's "hairy stone" fortress is one of the most well preserved Istrian castles.

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

A musical instrument played by the sea.

This historic timepiece is thought to be the only public clock in the world that keeps lunar time.

A former Latvian headquarters of the brutal KGB secret police is now open as a grim reminder of their atrocities.

A former imperial sea-fortress and Soviet prison.

Estonia's largest creative city is a vibrant bohemian hub located within a former industrial complex.

Spend your honeymoon where the Devil had his wedding.

This disappearing geyser has been attributed to witchcraft, but really it's all about rainfall.

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

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

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

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

One of seven Jewish catacombs in Rome and one of only two open to the public.