No one knows who built this strange cave of worship or exactly why.

Once the legendary capital of the Dacian Kingdom, this city has been reduced to mere ruins.

Home of the first female Hungarian poet, where her secret writing lay hidden for over a century.

The ancient Greek Titan guards this massive dam holding a lightning bolt to symbolize electricity.

Climbing to the top of the cathedral's bell tower offers sweeping views of these medieval ruins.

A stunning 18th century pharmacy and medieval chemist's collection.

Thousands of objects tell the story of a city famous for its tobacco.

Once the largest rope factory in Greece, this abandoned plant now stands like a ghost of industry past.

The largest Roman amphitheater in the Balkans once held over 20,000 people, but managed to lay hidden for hundreds of years.

This Croatian island is for sale but no one is buying due to the dozens of accused Nazi sympathizers who were massacred there after WWII.

This abandoned Olympic skiing facility still bears the scars of the Siege of Sarajevo.

A bridge destroyed three times: once as a ruse, then in an actual attack, and finally for the movies.

This unique structure allowed boats to bypass underwater mine barriers in the channel to enter the harbor.

A hidden stream deep in the mountains creates one of the largest tufa waterfalls in Serbia.

This iconic L.A. bookshop is housed in an abandoned bank—both symbolic and chic.

An artsy hidden staircase leads to breathtaking views of San Francisco.

Budapest's Communist-era statues, banished to the suburbs.