While we were there we discovered the remains of the Rose theatre. OK, admittedly someone had already discovered them, dug half of them up and built a visitors centre over the top, but still seemed a good find to us (although it says it's only open to pre-booked tours, it was open generally to the public on Saturday as a one off).
They're looking for funding to excavate it fully and then cover it in a glass floor and open it up to the public.