How did a low-key prison movie which was considered a box-office flop on its original release become one of the most popular movies of all time? Mark Kermode traces the history of this unexpected audience favourite from the pages of Stephen King's novella 'Rita Hayworth and Shawshank Redemption', through the icy corridors of Ohio's Mansfield Reformatory (whose imposing gothic architecture dominates the film), to the television and video screens on...