ROOM OF REQUIREMENTS
The Room of Requirement, also known as the Come and Go Room[1], is a secret room within Hogwarts Castle, that only appears when a person is in great need of it. The room is thought to have some degree of sentience, because it transforms itself into whatever the witch or wizard needs it to be at that moment in time, although there are some limitations. The way to open the room is to walk past it three times thinking about what you need, and the door will appear. It is advised that the users of this room be very specific about what they are looking for, as it has been shown that other people can enter the room and see what the occupant is doing if they know how the room is being used.