It means it's a weird house. If you are in the bathroom, there are walls on all four sides and a door. If you are in the darkroom, there are walls on all four sides and a door. You can go into those rooms, shut the door, and be alone. However, if you're in the kitchen or the bedroom (or any other room), there aren't any doors, you can see out of those rooms into other rooms. There also may be "half walls" (walls that only go from the floor to waist height) that you can see over.

thanks, i got it

To understand this you must first understand what the ceiling is. The ceiling is the wall that's overhead of you (if you're in a room right now, look up and you'll see the ceiling). The expression; walls that stretch to the ceiling basically mean that the walls are connected to the ceiling: they are so tall that they meet the ceiling of the room. Doors that open and close mean that those doors can be opened and can be closed (you can open the door and you can close the door: it's the only two things you can do with a door). To put the text in more easy English, one could say: 'Only the darkroom and the bathroom had walls that went up to the ceiling and that had doors that could be opened and closed. She had made the darkroom herself. The darkroom had stainless steel sinks for washing print and washing film.' I hope this helps!