If you will recall, our bathroom looked like this (above) a few weeks ago. We abandoned the heating duct which went to the bathroom upstairs and so far it doesn't seem significantly colder in that room. We continued with the demolition and removed the drywall and trim and cut through a couple of studs. I added a header to support the weight of the missing studs and framed out the new shower, which as you will recall is under the stairs and will get infrequent use.
Here's the newly framed space and you can see the fiberglass shower pan sitting under the stairs. Luckily, the new shower space was about 36 inches square by a little over six feet tall, and lo and behold they just happen to sell shower pans that are 36 inches square. They do not sell shower enclosures that size. We were going to have to make our own.
The old framing was covered with plaster and lath and no had insulation between the studs. This is one of the few walls that remain uninsulated (until a few days ago, anyway). They must have burned a lot of coal in the old days.
This is a view of the bathroom, looking through the front closet, which of course has louvered doors. The toilet sits just out of view and I can say with some authority, that it was rather embarrassing for a few days. Using the bathroom was very un-private, but at least we didn't have any guests and Fergus didn't seem to mind. On the plus side, you could use the toilet and easily monitor the coming and goings at the front door.
Today the auxiliary shower is all but finished. The shower and closet are separated and insulated and it is no longer an option to yell "Come in!" to visitors while using the facilities. The shower space only needs a shower curtain to make it functional. We used galvanized roofing metal for the shower walls, and while it may sound horrendous, it is quite attractive, in an industrial kind of way.