A long time ago I did the London Loop ending at Coldharbour point, the boundary of Greater London. That was as far as the loop went then but it has since been extended to Purfleet passing these old concrete barges that were dumped there after the war.
The loop follows the Thames at this point and includes the RSPB bird reserve which served as a convenient stopping point for coffee and scone or soup.
This building is just on the edge of Purfleet, where there is a military heritage centre and lots and lots of new flats. Come to think of it there were lots of new flats in Rainham too since I was last down that way - Messrs Chuckemup, Builders and decorators have been at it again.
The picture shows a surviving gunpowder store that hasn't been converted to flats.