The best option is to rent a motor boat and take a tour of Lake Atitlan, visiting some of their villages. We suggest: Santa Cruz, San Marcos, San Pablo and San Pedro, and coming back, San Antonio and Santa Catarina. Before returning to Panajachel, ask your guide to the hot springs of the lake, a point on the shore where the water comes hot from the rocks. For swimming, but with high tide and calm. Negotiate pricing, better in groups.