Here are Victor's pictures of the coastal area around St. Just. (Remember, the pictures I posted were exclusively those taken with my iPad. I didn't have a way to transfer pics from Vic's high-resolution camera.)
This (above) is probably a mine chimney.
The presence of so many ruins everywhere is, to me, reminiscent of Detroit. I was just perusing a book of photographs of empty and ruined structures in Detroit. It may be a modern-day equivalent.