It was located on a college campus. Doesn’t really speak well of the college, but times were lean.

In later years this was converted to a music building; I took piano lessons here in the late 60s. Mr. Froelich taught in the room on the right; the recitals – the terrifying, sweat-soaked recitals – were held in the room on the left. All traces of its former life as a library had vanished. Except for the smell of old books, of course. Worse than that: old unread books, tomes that had never been checked out at all, and now haunted the rooms, shouting with mute fury. 

No, it was mold. I'm going with mold.