This former estate of a fascist leader is now a burnt out ruin leading to a system of secret tunnels.

Humble beginnings for one of the world's most famous scientists.

This Croatian fairytale castle is slowly falling apart thanks to years of neglect.

Gargoyle head that brings good luck.

Once a state-of-the-art tuberculosis treatment spa, these ruins are now ruled by paintball players.

This truly palatial work of Communist-era architecture now sits crumbling on a Croatian beach.

This huge metal monument is slowly being stripped to its concrete skeleton.

Legend has it fairies gathered at the site of this medieval castle.

The complex has been abandoned since the Croatian War of Independence, barring a stint as a set for 'Game of Thrones.'

The remains of a sunken military ship wreck visible through clear water.

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

This stunning, out-of-the-way Croatian monument commemorates a community's uprising against occupying fascist forces.

Where the lovelorn find a home for their sentimental keepsakes.

A musical instrument played by the sea.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

An ethereal glowing blue ocean cave in Croatia.

This graffitied 19th-century building was a prototype of European industrial architecture.

150 or so scrounged-up lamps, chandeliers, and lanterns light up this alley in central Athens.

The only surviving choragic monument is a trophy awarded in 334 BC for the winning dramatic chorus.

This historic structure has been used as a mosque, a barracks, a prison, a school, and a bakery.

This once architecturally advanced housing complex is now a haven for squatters that still bears the scars of war.

The ruins of an ancient mansion sits in front of and underneath a contemporary art gallery.

A preserved portion of an ancient Athens barrier is displayed in a hotel basement.

The site where hundreds of Greeks were tortured by the Nazi secret police is now a cosmetics store.