Well, I can't find the map I am looking for so here is a google map terrain view.
https://maps.app.goo.gl/mY96EavYSZz26WwX9
So...you park in one of the lots near the VC. From the VC there is a "land train" that takes a paved lane out to the stones (or you can walk) then coming back I always walk back via the Barrows, the Tumuli and the Cursus on the other side of what is noted as Fargo's Wood. You can see the walking paths in the aerial view.
You can also download an Audio Guide to your phone before you go (so be sure you have your earbuds with you!).
https://www.english-heritage.org.uk/visit/places/stonehenge/plan-your-visit/stonehenge-audio-guides/
Oh yea, and I just found the map I was looking for in the Transcript of the Audio Guide.
https://www.english-heritage.org.uk/siteassets/home/visit/places-to-visit/stonehenge/plan-your-visit/stonehenge-landscape-tour---audio-guide-transcript.pdf
It's also possible to walk from Stonehenge to Woodhenge and Durrington Walls via public footpaths. You can see the paths on the google map view as you head toward Larkhill housing area, skirt around the bottom end and head to Woodhenge.
And will add regarding the amount of time Bletchley Park takes...I agree I spent most of the day there. Look at the train times ahead of time as there are some that are direct to Bletchley and some that have lots of stops and take longer so you'll want to get the train departure that is direct. IF you get there when they first open, be sure to sign up for a free tour that is given periodically. You'll still have time to go back to places you want to explore further after the tour.
And back to Stonehenge and the Neolithic landscape....I think for one thing there are just not that many Neolithic sites to see in the US so it's a real treat to see those things in a landscape. I've been to a site here in Idaho that has been dated to 9,000 or so years ago (from the soot on the rock shelter roof) BUT it's been backfilled to keep it from being damaged so you can't see it properly. There's another that I'd like to get to (Medicine Wheel in the Bighorn Mountains in Wyoming from about 3200BC) but it's fairly remote and is a sacred site to the local tribes so depending on time of year is reserved for ceremonial purposes. So...I try to "fill up" on Neolithic sites when I am in Europe. I've been to many in UK and France and honestly will return again and again.