It appeared on the seventh floor in the corridor to the furthest left of the castle. It appeared whenever a passerby, or a user of the room actively needed something. It could produce broom closets, huge warehouse-style type rooms that held items collected over years, even in a time of need, it produced a tunnel all the way to Hogsmeade Village when Harry, Hermione, and Ron needed a way into the castle without causing a ruckus. 