Portovenere offers a lot to see to the day-tripper, but you might want to spend more time here. There are many hiking trails on Palmaria Island, a Regional Natural Park; a small boat will take you there from Portovenere in minutes. You can visit the recently restored 19th-century fortress of Umberto I which has been turned into a civil/military museum of the Mediterranean. You can also explore the blue grotto (only by boat) or just lay on the beach where the boat from Portovenere leaves you. In the summer, Portovenere is served by boats from the Cinque Terre, La Spezia, and Lerici. Walking all around the small island should not take more than half a day.
To get a good view of the surroundings and a good bit of excercise, take the trail from Portovenere shown in green on the map. Called The High Path Sentiero 1, it peaks at Santa Caterina at 450 meters above the sea. You'll find the trailhead well marked in a piazza near the tourist information center. More on Senteiro 1.
Read more about the village of Portovenere in our Portovenere Travel Essentials and Profile.
A short distance from Portofino and accessible by bus is Le Grazie, a fishing village turned seaside resort where you can visit the Ex Convento degli Olivetani with 16th century frescos. Nearby are the remains of the Roman Villa of Varignano, showing some ancient thermal bath technology in a wonderful seaside setting.