Meanwhile, the well is officially 53 feet deep and I'm trying to arrange with a proper climber to pop me down to have a look about. A brief video survey (i.e. a video camera on a piece of string) revealed some intriguing hints... Was that a hand print on the wall? A scrap of cloth on one of the beams? A curved, iron-age cutting blade?
Keep watching for next thrilling episode. (BTW, I haven't forgotten this is supposed to be about a studio build but right now the well is by far the most interesting thing going on).