The door opens easily, and you walk in and shut the door after you. Rather than a classroom, it looks like you're in a library. There's a lot of, to be honest, weird books all over the place.
I made a mistake with the hall description earlier on. It has been fixed. There was an office-like (though not main office-like) room 100 near the stairs and rooms 101, 102, and 103 in the hall you were just in.