Powder room toilet.
Now, there's a bit of a story here. It seems that two owners back the decision was made to expand the kitchen. In order to do that they had to close off the original entrance to the powder room. So they did. And they didn't make a new one! So there was a room, with a toilet and sink, all closed off behind walls, for years. Until the most recent owners decided that there should be a way to get from the house into the greenhouse. In order to get from the sitting room into the greenhouse they had to make a hallway through the closed off powder room. They wanted a powder room too, so they deicded to revive it. They put a toilet in the old doorway (still framed) and put a door on that. All that's in that room is a toilet and a roll of toilet paper. The original tile is still in there! Across the hall is the sink. You go between these two to get to the greenhouse.