Suggestions for somewhere pleasant to ride where we can make a four or five day circular route in the UK

[theoldpatagoniaexpress]

Not too hilly (on final leg of recovering from knee surgery). No further south than Cambridge, not Norfolk as we are going there in the near future.

Can anyone suggest anywhere nice to ride, quiet country roads, lovely scenery, NT/EH places to see/coffee shops galore.

We are a bit stuck on the avoiding hills bit.