Park Hill, a huge concrete-framed modernist social-housing scheme, was completed in 1961 when Sheffield had near full employment and young architects - in this case Ivor Smith and Jack Lynn - were developing new ways to satisfy the need for affordable flats for rent. Since then the national housing scene has been transformed, a change embodied in the fate of Park Hill, stripped back to its frame and recast for, largely, private ownership. Keith Collie's photographs capture the cliff-like grandeur and formal beauty of this massive structure in ruins and the epic scale of the renovation. David...