Janitor's closet:

The Janitor's closet is found where all janitor's closets usually are. Under the stairs. In this case the closet is under the stairs that lead up towards the alchemy labs. In general the alchemy labs need the most maintenance due to the high level of explosions that occur there and so being close (but not too close) is an advantage.

The closet itself doubles as an office. It's very narrow but stretches back under the stairs. In fact… it stretches back a long way under the stairs. From the door you can't actually see the far end and the place where you'd expect the wall to be just isn't there.

There is a narrow desk to the left just as you enter with shelves above, below, to each side and behind, stretching back into the dark. On the desk is a glowing warm red coaster with an ever hot cup of tea on it, as well as an assortment of half completed repairs. On these shelves are boxes and in these boxes are practically anything you can imagine that might ever have a use fixing something. String, screws, eyes of newt, elbow grease, spanners, magical glue, emergency custard creams, skeleton keys, skeletons, universal solvent, mops, buckets, jars, tins, paint… the only problem is finding what you want, when you want it.

The only person who really knows their way around the closet is the Janitor. His name is Mike and it is widely reported that he can fix anything if he sets his mind to it. As far as anyone can tell he has no talent for magic - just an excellent ability to fix things. No one has seen Mike for a while though - most likely he's found a quiet corner to hide in away from the demands of the teachers.