A tower marking the spot where Yugoslavia began its resistance against the invading Nazis stands neglected, but not quite forgotten.

When Croatia became independent of Yugoslavia, the splintering governments left behind these concrete tunnels.

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

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

Croatia's towering concrete blossom grows from the site of a World War II concentration camp.

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

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

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

Longest fortress system anywhere in Europe.

This scale model of our solar system hid in plain sight for years before a physics team sought out all the planets.

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.