I would look to the rooms around 9,13 to find a way in :)
Hint (possibly small spoiler): If you leave a room in two different ways at the same time, you will be teleported 5 rooms above. Depending on how far you are in the game, your only have experienced this in one way (leave room 10,12 both to the left and to the right simultaneously) - but there are also other ways.
Good luck!