Notice how cleverly the camera followed Barnabas and Ben Stokes right off the edge of the set of the Collinwood foyer, keeping the lights around them dark, as they walked to the "door" leading to the "study." This is one of a few times when we see someone do that, despite the fact that there seems to be no connecting set between the two locations. Usually when one of the characters goes to the study, we see them walk out of camera range, downstage left, and sometimes downstage right.
Have you ever imagined what those missing parts of the sets might look like? The other side of the Collinwood foyer, for instance; what one might see looking straight ahead if they were walking down the staircase. I've always pictured an enormous hallway leading off to the study, perhaps a library, and who knows what else.
And what of the other side of the Old House drawing room? Or the other side of Maggie's cottage? What do you suppose they might look like?