Dave, The tunnel I mentioned ran from Ketts Cave, Under Silver Road Mousehold Avenue ,coming out at the bottom of a very large chalk pit at the rear of the Catholic church on Sprowston road. Long since filled in and now partially built on. A neighbour of mine some time ago was relating to me how her mother had been driven through there on a horse and cart many years ago. I would imagine that that must have been one of the longest in Norwich ,(unless you know otherwise). The city engineers dept. confirmed that this tunnel did exist. Derek.