Hagioscopes ... one possibility is it was a Leper's Squint through which lepers were able to follow the service and take communion while remaining outside the Church. Others believe that it is an Easter Sepulchre; used to recreate the Easter mystery at a time where visual imagery played an important part in worship ... this one is in St. Wilfred's Church at Ribchester, Lancashire and has been used for the purpose of Easter - I don't think there are many lepers in the village nowadays !!!