Stonehenge itself was really, really cool. Our bus tickets included entry to the site and free audio guides to the site. You walk around the stones, and there are markers along the way that tell you when to move on to the next section of the recording. Seeing this was definitely the highlight of my week!
On the way back to Salisbury, the tour bus stops at the ruins of a 12th-century castle that you can visit if you want (also included in your bus ticket). We did that as well. On the way up the hill to the ruins we made a new friend:
And here's one of the medieval streets of Salisbury: