When you walk to the end of the Canal Basin on the opposite side to the shops there is a brick plinth about 9 feet wide, 2 feet thick and about 9 feet high on the side of the canal. What is it or was it?

Also what was the chimney for thats on the same side as the shops but again at the far end over the wall? It's not attached to anything now.

If you are refering to Victoria Keys, or Sheffield Harbour (makes me laugh saying it), the large building, red bricks above the water is an old wharehouse, boats woud go underneath and be loaded from above. there are info leaflets if not visits organised from there.
you can also find info on the Hedgerow postcards you'll find around ton, there's a little story at the back.

Thanks captain_scarlet, but I don't mean the wharehouse.

The plinth thing is found by - going over the little bridge over the old dry dock, turn left by the Office, go along about 80 yards and its at the side of the water.

The chimney's on the other side of the canal, same side as the shops but further along on the left after the pub. It's not actually on the canal side it's over the wall but you can see it becuse it's so tall.