I think it has one of those door doors just put of shot. When house buying I.saw a few that had converted the lean-to into a toilet and the upstairs toilet into another room. Some had this configuration with a door to it from the kitchen. One had you going outside to use it and, considering it had the only bath and shower in the house, that'd have made for an invigorating stroll during Winter.
It wouldn't slide to the left (in the picture) because there are electrical outlets and lightswitcbes in that wall. It might slide to the right, or there might well be a regular door just out of sight on the right.