Mr GBT and I do our best to do something if we find we have a day without any commitments at the weekend. What we do varies according to time of year, weather, budget etc, but walking is always a favourite. The Fancy Free site of straightforward walks has already come up trumps on a myriad of occasions and has become my go-to if I'm lacking inspiration/ideas. On our last most recent free Sunday we opted for one of the Surrey walks around two villages. We live very close to the border so it was no distance for us to get to the starting point and to the best of my knowledge I've never been to either!
Newdigate and Capel. Within spitting distance of one another, but both with a completely different feel.