We were misled into taking a 18 euro bus tour instead of the free shuttle. It worked out OK. Plenty of bars for free wifi, good coffee , nice cakes ...
We made our own city walk and it was well worth it. It's a bit of a climb just outside of the port but there are things to see and as with most climbs the view made it worthwhile. There is an excellent, barely restored Roman Amphitheater on the hillside as well as a couple nice cathedrals. The inevitable shopping street was decent and the public bathrooms under Saint Remy are (no exaggeration!) ...
I got up early and took a bus from near the port to the top of the Castello (old part of city). Then I walked down to the terrace at the fortress, seeing things along the way and taking pictures. Then I met my husband near the port and we rented a Smart Car from CarBusTec, a local company nearby. We drove to see the lighthouse down on the peninsula, the flamingos on the way to Poetto Beach, and ...
Plenty to see in Cagliari. We again did our own thing with very helpful Tourist Info who not only provided a map but suggested a route to take in all the main sights. Lovely palace (home of the viceroy) next to the catherdral - well worth a visit - small fee - try to catch the English speaking guide. ...