Yes I know I can still do a shift-command-g to /Volumes, and there it is, at jenny-imac/APPLE SSD/Volumes, which of course is normally invisible. And when at jenny-imac/APPLE SSD, I can hit command-shift-[period] and then see the (really invisible) "Volumes folder.
I just wondered why this visible one had appeared in my User folder.
Well I shall be bold, trash it, and re-boot.