The original Rosenberg House is in the left rear. Rosenberg’s boarding house was so successful that he built the Hotel Rosenberg in 1896 to accommodate his increasing clientele. This very early photo is circa 1896-98. Note that it is not yet attached to the Howland House on the right. – Also, the original “house” is only 2 story.
A question was asked about the elevator in the building. It is a 1939 Otis elevator much like the one in the photo below. It has 7 stops. Because the hotel is actually 3 buildings joined into one, the floors are join at different levels. The elevator has doors on both sides. When it stops on the Howland House side, the doors open on one side. When it stops on the Rosenberg Hotel side, it opens on the other side.