Nonsensical hallways that go on forever, or exit the way they entered. An entrance that, when the party tries to leave, just leads to more of the building. Narrow window slits in the tops of hallways that just let the slightest sunlight in, and then remain dark longer than any night could last.
A ghastly surgeon who prescribes lobotomy for anyone he encounters, and attempts to force one on them. Accompanied by hulking, expressionless orderlies, who themselves have the affect of a lobotomy patient, possibly formerly non-hostile NPC patients.
Inmates who babble about demons and Hell, only for you to later find occult paraphernalia and ritual sites.
Tales of troubled patients that committed suicide, only for you to later find them in similar circumstances. Hearing of a patient who cut her wrists in the bath, and then later finding a tub filled with murky reddish liquid and chalk-white fingers hanging on the edge. Being told about a patient who bit his tongue, and then later finding a trail of black slimy blood leading to a rotten tongue with bile dripping on it from above (don't look up!).