I definitely suggest taking a stroll in Calasetta. Beside the city main square, a lot of nice streets will make the perfect scenery for a relaxing walk back home after a day spent sunbathing.
Remember to climb up to the tower (visible from everywhere!) to enjoy a panorama on this small city sourrounded by a wonderful sea :-)
There are so many Torre's around the South and Southwest of Sardinia that we burnt out on them. Our favorites were the one at Tharos in Cabras and Nora nearish to Cagliari, but there are many with good views from all of them.