That sketch drawn by Rheims would have to be the forward lavatory block, imperfectly remembered. The transverse passageway in which the door was located is shown to be continuous with the passages which extended from the main fore & aft corridors to the inner windows of the promenade deck. These passages were in fact a short distance further aft and not visible from the lavatory passage. Probably what actually happened was that Rheims came through the lavatory door, turned right (as he recalled) but did not immediately see the iceberg. Rather he walked for a few seconds to the main corridor and a short distance back along it towards his cabin before looking to his left as he passed the short passage leading to the window. At this point he would also have been able to look back through the window at the forward end of the main corridor - "I also saw the iceberg this way and that way forward to the starboard side and at right angles from the starboard side". Bearing in mind the events that followed and that he was trying to recall these details 18 months later, it's understandable that in his recollection the sequence of events at this relatively insignificant stage of the proceedings would get slightly compressed.