So you don't want the room to be actually usable? Even using moveobjects, you will still be able to use the door. You could place the door and then use moveobjects to place something directly behind the door, that way Sims would not be able to go through. Then you could use one of the tomb tools to make the room hidden until someone enters, but because they can't use the door, they won't be able to enter and so the room will always remain blacked out.