In reply to judethesaint:
https://www.nationaltrust.org.uk/bath-skyline/trails/bath-skyline-walk
Places that are generally nice to potter around for a couple of hours - Blaise Castle, Frome Valley (Snuff Mills), The Downs in Clifton, Ashton Court estate, anywhere in the Mendips (Cheddar Gorge, Blagdon Lake or Chew Valley Lake, etc.).
The Strawberry Line is great (http://www.thestrawberryline.org.uk/). I've not the smaller sections but I got the train to Yatton and walked to Cheddar. That was a good, long jaunt.