Salisbury exists, in the visitor’s mind, as the place near Stonehenge. The city is better than that job description. The cathedral has the tallest spire in Britain, a close of grass and houses that is one of the most complete in the country, and a copy of Magna Carta if documents interest you.
Use it as the night before or after the stones, not as a service station. The stones are a timed visit on a plain to the north. The city is the walk, the close, and supper.
See
The cathedral and close
Allow longer than you think. The spire is the skyline. The cloisters and the chapter house are the interior. Walk the close even if you do not go in.
Stonehenge, separately
Book a time. The visitor buses leave from the station. Go early. Do not bolt it onto a cathedral morning and a Bath evening.
A river walk
The Avon watermeadows below the close, the view Constable painted. Twenty minutes and the right scale.
Old Sarum
The abandoned earlier city on the hill to the north, if you have the afternoon and want to see why they moved.