I thought that there was a drive along the top of the terrace.
Sometimes in these old photos the proportions are deceptive, and although it looks like the width of a walking path, it may actually be wider. Or maybe there is a drive above the small top terrace behind the seats?

I don't think the other side of this building would have been the main entrance as there is the side of the house behind it, and not a grand enough entrance. However there may be another entrance on the left which is not visable.
I do wonder why someone would take a photo of the back or side of such a building though.
Further to my comment about depth of field and the illusion seen in some of these photos, I am wondering if the greenhouse is actually further back behind the house, but only appears to be on a similar level to the house. I also think the photo was taken not exactly in line with the front of the house, but from an angle, hence being able to see the greenhouse. If it had been taken directly in front of the stairs, the greenhouse may not have been visible.
I do agree that this house has been added to over the years, but they have tried to tie it all together style wise. I still find two entrance doors so close together odd ......
Still, those comments are no help in locating it.
