It has been likened to a monster, an oil rig – and the Parthenon. Now, for its 40th birthday, the astonishing London landmark has joined the Open House festival, to grant admirers a rare look around the inside In his 2012 book A New Kind of Bleak, the critic Owen Hatherley called it “monstrous, compelling” and utterly messed-up. Back in the 1980s, a then…