What's the room of requirement? One of the characters in the book describes it as "a room that a person can only enter when they have real need of it. Sometimes it is there, and sometimes it is not, but when it appears, it is always equipped for the seeker's needs" (Harry Potter and the Order of the Phoenix, Chapter 18)
Chang's tiny apartment can transform into 24 separate spaces, depending on his current need.
You can check out photos and all of the possible configurations in this article from designboom architecture.
