There's is a room, a room that opens anywhere just once, for one person only, and trapped them until the whim of
the room allows it. The room changes to fit anything (and anyone) as it needs, but there are three constants:
The entrance door, the exit door and a simple book which the room uses to communicate with whoever is inside.
There's always someone at the room, since some other has to take it's place before leaving. Who's the person in
the room?
(Basically is a any character from anywhere with any character from anywhere kind of deal, each new chapter has
the previous person leaving and the new one staying and meeting someone else)