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

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

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

A war-torn Olympic relic is being overtaken by graffiti and nature.

Yugoslavia's biggest underground airport lies in ruins.

A Museum of Psychiatry in a still-operating mental institution.

This abandoned Belgian fortress is purposefully being left to nature.

This ghost town in Belgium will lose its street art when it ceases to exist.

The townhouse where the "Blood Countess" Elizabeth Báthory started her murderous career.

The personal charnel house of Anton Bruckner.

The former private quarters and office of Dr. Sigmund Freud now hosts a museum housing the works of the founding father of psychoanalysis.

Terrifically morbid cemetary and site of famous Paracelsus' grave.

Macabre museum devoted to historical Viennese murders.

The crypt of the imposing Stephensdom holds royal intestines and thousands of skeletons.

This cavern was used as a hidden hospital and safe house during the Vietnam War.

This Vietnamese hell cave lets visitors take a walk through a devilish underworld full of demons.

Vietnam's feral abandoned water park offers access to a post-apocalyptic funscape, now with fewer crocodiles.

Derelict airplane bodies serve as both home and income for three Thai families.

A rare pod of derelict midcentury Futuro and Venturo houses lines a semi-abandoned beachfront resort outside Taipei.

The abandoned hospital whose elaborate ghost stories cover up the dirty truth - an uneventful sanitation issue and other mundane reasons for its demise.

Plenty of old carney magic still haunts this photogenic amusement park.

Hundreds of wooden coffins dangle from cliffs and caves in the Philippines.

This abandoned-looking amusement park is frighteningly open for business.

A boat ride through utter darkness, lit only by headlamps, reveals an emerald green pool locals believe is sacred.