Sophie Gordon has put together a nice summary of loops that can be ridden on gravel trails and quiet lanes in north-east Norfolk. The longest one (between Norwich, Reepham, Aylsham and Hoveton) features Marriott's Way and the Bure Valley. The hilliest one is on the north coast between Sheringham, Cromer, Holt and Morston. There's the Great Wood gravel ride from Cromer, plus a couple of shorter loops from the Hoveton & Wroxham cycle hub.
Read all about it on the Cycling UK website!