Now - this isn't a conventional UK tourist outing but as someone who was born in Norfolk and has been back a few times to visit - a day out on the Broads is a lot of fun. Rent a boat and just cruise.
https://en.wikipedia.org/wiki/The_Broads
http://www.visitnorfolk.co.uk/explore/Broads.aspx
http://www.waterwaysholidays.com/norfolkbroads.htm