This magnificent abandoned hotel has long been haunted by its Nazi past.

An abandoned resort in North Macedonia is a relic from the Communist Party of Yugoslavia.

The decaying remains of a once-luxurious Soviet spa town.

A 1970s resort city now stands abandoned, caught in the middle of a divided island.

Colorful concentric circles honor a small Croatian town's supposed spot at the nucleus of it all.

Island wonderland for communist autocrats.

Built as an anti-fascist tribute, this surreal Yugoslav memorial became an unwelcome symbol after the Croatian war for independence.

This abandoned Croatian stronghold never saw a great deal of conflict but it is still a beloved relic nonetheless.

The only gulag ever to exist in socialist Yugoslavia.

Now abandoned, the world's first torpedo factory is crumbling into the sea.

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

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

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.

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

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

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

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

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.

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

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

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.