Longest fortress system anywhere in Europe.

The now-overgrown beach resort was once frequented by Yugoslav military elite.

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

A wunderkammer of gold and silver reliquaries and ancient saintly bones.

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

This picturesque medieval monastery guards a small trove of historic treasures.

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

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

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.'

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

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

Yugoslavia's biggest underground airport lies in ruins.

A wonderfully strange collection of 500+ stuffed frogs doing people things.

Where the lovelorn find a home for their sentimental keepsakes.

An ethereal glowing blue ocean cave in Croatia.

Formerly Yugoslavia's "forbidden island," this sleepy little city still holds the abandoned remains of military strongholds.

A Bibliophile's Dream.

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

The world’s oldest and biggest bookstore stocking only mystery, crime fiction, espionage, and thrillers.

The world's oldest bookshop still in operation.

Mirrored floors and arched shelves create the illusion of an infinite tunnel of books.

A cozy bookstore is tucked within an old gold mine shaft beneath the cafe and ice cream shop.

The beloved home to all publications indie, erotic, and punky.