If you do visit the cathedral, there are small group tours to see the construction of the vaulted ceiling. The timber framing is amazing, especially the chapter house's. As you climb the stairs to start the tour, a full view of the nave, with the rose window behind, may make you dizzy.
The tour is 5 quid (may be more now), the best value I've ever paid in England.
Unfortunately I missed it yesterday and today Sunday no tours, so am visiting the castle. There is a tour at 11 am. Then to Boston (the original!), Kings Lynn, Ely Cathedral