One of the best things to do in Positano is to get out on the water. Small motorboats can be hired by the hour from the beach, or you can join one of the day trips to nearby beaches and sea caves. The boats can reach hidden beaches inaccessible by land, and the perspective looking back up at the town from the sea gives you the full drama of the cliff face.
Day trips typically go to Li Galli, a cluster of three small islands just south of Positano with a lighthouse and ruins. The islands were bought by the dancer Rudolf Nureyev in 1988, who lived there until his death. You can also take a boat north to Amalfi or south to Praiano, exploring the coastline at sea level.