The place we stayed in Sarlat FR had an almost open concept bathroom. There was a window that looked out over the street with a cotton drapery that was not giving much in the way of concealment. I’d brought along some binder clips and used them to attach a towel to the drapery to block out most of the view.
If I’d brought the forgotten duct tape or painters tape, I would have first taped the curtains to the walls and then attached the towel.