Our favorite "excursion" is spending a day at Chileno snorkeling/sunning. We bring our own snorkel equipment and have a rental car, but there are boats that take people out there too. Sunset cruises are very popular. We did the Tropicat and really enjoyed it. It's not your typical wild
booze cruise, but they do have beer, wine, food. Also, the desert ATV ride is fun if you like that ...