The title of this article is conjectural. Although it is based on canonical information, the actual name is conjecture and may be supplanted at any time by additional information released from canonical sources. If this occurs, please move this page to the appropriate title.
There is an unused classroom on the first-floor corridor of Hogwarts Castle. It now seems to be used as a storage facility containing books, chairs, desks and several boxes.
Behind the scenes
There is a multiplication on the blackboard of this classroom. This seems to suggest Maths or any Maths-related magic (such as Arithmancy) was once taught in the classroom, but alternatively a student might have written the operation on the board (this is supported by the hat sketch and the doodles). This means that it could be the Advanced Arithmancy Studies classroom, known to exist on the first floor.