The construction of the Zagreb university hospital started in 1985 and lasted until 1992 when it was halfway completed. Since then it's abandoned and every year it gets worse - most of the metal was scrapped by thieves and some areas have completely overgrown by weeds and trees. The total investment in the hospital was 157.000.000€
At the start of the project the hospital was supposed to be a regular hospital, build in order to match the increasing population of Zagreb. But at some point during the construction it was decided that the hospital will become an university hospital centre - and the project was scaled up. Operating rooms were enlarged, student areas were added and the building size grew while te cost was not taken into account. At that time the project was presumably scaled because of rivalry - there were already two university hospitals in Yugoslavia, in Ljubljana and Belgrade but not in Croatia. When Croatia established independence from Yugoslavia and the war started all resources went into defense of the state and the project was put on hold. For years and years the city government delayed the resuming of the construction and eventually it came to the current state.
Now the hospital is in very bad state and it would take a lot of money just to resume it's construction. It's also deemed too large to mantain by the Croatian association of civil engineers. The best course of action would be to either tear the site down or to try to restructure it into something else. However, the situation is unlikely to change. The politicians know no one wants to hear the hard truth so the hospital issue is always avoided. Until someone makes up the courage to deal with the past mistakes the hospital will sit there, slowly deteriorating into a ruin.
Important: There is a possibility that will be a security guard at the location, although I haven't seen any.