After uncovering the wall behind the cabinets, I decided to look inside the wall. You know, just for fun. First I removed a piece of gypsum board that was just nailed in place. I found some insulation material stuffed in the hole.
I removed the insulation material. Yup, that's a hole in the wall.
You can see the plaster and lathe in the opposite wall (which forms the guest room).
I stuck my camera down in the hole. There's some wiring running up the wall for the over-the-sink light. Otherwise, not much to see.
Medicine cabinets in the landing, awaiting their fate.