Center Parcs.
That's where I'm thinking of going.
Or if you've got a few days, a car, and plenty of money, just go for a drive. I did that a couple of summers ago, and it was the best 3 days of my life, very relaxing.
Course, not everyone finds driving relaxing so that's up to you.
Lake District - lovely scenery, peaceful and some great steep roads to keep you on your toes, ie Wrynose Pass & Harknott Pass.
My favourite place in England.