Stretching the concept of "abandoned," but having the hospital serve as an asylum or dumping ground for patients in various stages of abhuman mutation could work well for a WoD or DG game. The place is boarded up from the outside and appears empty, but the inside is a cross between a hospice treatment center and a prison.
People who are showing early signs of mutations are brought here and reside on the lower floors, they're mostly cognizent of what's going on and have various degrees of acceptance. Most are there against their will, but it's tempered with a warning of what their state will progress to and a false promise of finding a cure for their condition. Mutations manifest in a number of ways, such as abnormal growths, extra sensory organs beyond what humans naturally have, future sight, etc, some effects beneficial but mostly negative.
As you go up on the floors, the hospital is under higher security and more strict scrutiny as the patients are in more advanced stages of mutations, accompanied by mental breakdowns either induced by the mutations or just as a natural consequence of the psyche snapping as one's form is changed. The patients can be dangerous and are aware enough to want to escape, requiring constant monitoring by the staff.Basement floors are complete lost causes, things that were once human roam the grounds and prey upon each other; the basement has become its own ecosystem. Contrary to the rest of the hospital, the basement appears to have been renovated specifically to contain more dangerous patients and goes down several floors, but at some point due to a breech, the entire thing had to be sealed off and abandoned. It's filled with hyper deadly inhabitants that follow no natural biological rules, and indeed the basement itself is partially living as one patient was warped into a bizarre plant-like entity whose spread her carnivorous vines across the entire place.