Quite correct Hollins! It is the (only) room in the Pin Mill (SteveH was in the right area!). The walls are all wood panelling, and the room is being restored - the footprints are those of the contractor (not a gardener!) who was making some minor repairs prior it all being cleaned and polished. The plan is to open, on a limited basis, for visitors to view next year - narrow stairs and low headroom in the doorway will make it restricted viewing.
Here is a photo of the inside of the room itself, the window looks out over the Canal Terrace.