London to Salisbury to Stonehenge

This past October, I took the train from Waterloo to Salisbury and then the Stonehenge Tour bus.

https://www.thestonehengetour.info/

It worked out better than I was expecting. This is what I wrote about it in my trip report:

It involved walking to the Waterloo train station to take a 1.5-hour
train to Salisbury. I had booked us open return train tickets in
advance. There are no seat reservations on this particular train. Then
right outside the Salisbury train station, the bus picked us up and
took us to Stonehenge. The bus ride is not time specific, so you can
take any bus you like. We took the first one at 10 am. The check-in
process was a little slow as it seemed most people had not purchased
tickets ahead of time. (I bought our bus and Stonehenge tickets ahead
of time from the tour website linked above.) The bus dropped us off
near the visitor center where we had to show our tour tickets to get a
Stonehenge ticket. We then took the free shuttle out to the site. We
had a fantastic day!! Blue skies!!!! It was not crowded at all. And
much to my delight, there were sheep all around. I had originally
planned for us to see the Salisbury Cathedral afterwards, but it was a
long day and so we decided to just head back to London.

https://community.ricksteves.com/travel-forum/trip-reports/10-days-in-london-our-first-time-a-trip-report

So, we had purchased all our tickets ahead of time. It just makes things easier. And the train tickets are cheaper if you buy them in advance. The way there was for a specific time, but we could take any train back. We had first class tickets. As there are no seat reservations, we thought 1st class would be less crowded, and it was.

For being “just rocks” as you call them, they are pretty incredible.

There is no main line engineering work that day affecting your journeys, and none currently planned on the tube network.

If you book now Advance Train Specific fares are £9.70 each way in 2nd class and £16 in 1st class but those fares are dynamic.

It is important to stress that this is no service 1st class. All you get is a slight!y better seat. No lounge and no food and beverage.

You could go to Salisbury Cathedral afterwards where there should be Choral Evensong at 1630. I say should because I don't know how rigorously they observe the Church's year. It being Lent there is a small chance Evensong could be replaced with said Evening Prayer.

This is via South Western Rail, correct? An open ticket would mean I could leave at any time, right? Thank you in advance.

Yes, South Western Railway.

Being a Sunday a Super Off Peak Return for £43 is the 'open' ticket- use any train in both directions.

Or Carrie referred to the Semi Flex Return for £40- a specific timed train outbound, any train on the return journey.