Take a stroll around Whitlingham Broad, on the doorstep of Norwich. It's about 2.5 miles walk around the large Broad, plus there are loads of little spots including Whittlingham Marsh which is right up the end just before you go under the A47. There's a nice (short) 30 mins circular walk around the marshes where you can see some pretty rare butterflies, and on the walk back you go under the A47 which can be quite hairraising when a lorry comes over!
The parking does cost money now, but there are places you can park for free (they put signs up to make you feel guilty, but don't let that put you off!)