Can you suggest some contenders for day trips from YOUR home station - in the early summer, when we're less locked down but while accommodation away (apart from self catering for single bubbles) is still unavailable.
Red rag to a bull grahame, Bristol is spoilt for choice.
The recommendations from London on the link you have provided already had included Bath, Oxford, Weymouth and Winchester, which are also obvious ones from Bristol so instead:
Penarth, stroll from the station to the interesting high street with it's Victorian Arcade and descend through Alexandra Park to the waterfront and pier. From there a signposted route takes you over the headland then down to Penarth Docks and the Cardiff Bay barrier which takes you to the former Tiger Bay, Welsh Assembly Building and Mermaid Quay. A stroll past the Wales Millennium Centre takes you to Cardiff Bay station for the return leg.
Alternatively:
The Taff Valley Trail. Various railway stations to start from , for example, Radyr or Taff Wells, depending on how far you want to walk. Don't miss detouring slightly to include Llandaff Cathedral and "village". This general route provides various different routes to take other than the "official" route so it's good and different a second time around. Return from Cardiff Queen Street or through Bute Park to Cardiff Central.
Or why not?
Dawlish/Teignmouth. Station's at Teignmouth, Dawlish, Dawlish Warren to start and finish from. All stations linked by coast paths so you can tailor your day out to where you want to explore and how far you want to stroll.
There are others of course, Yatton for the Strawberry Line cycle and walking path and Great Malvern for the Malvern Hills. Gloucester is worth a visit for the docks, Cathedral and more.
Believe me, I could go on.