Rimini on the Italian Riviera
During the time that we were there, a festival called Rimini Beach Festival was going on so there was plenty of food stands, music concerts and people who were there to visit. The 15 kilometer long beach was full of people in sunchairs, playing volleyball or renting out kayaks, wind surfboards and scooters.
Rimini is also the Italian city which is closest to San Marino so frequent buses run, there costing 5€ and taking 45 minutes each way.
Although the city also has some historical monuments and a nice little city center we spent most of our time at Sunflower hostel, walking along the beach and driving around on our rental scooter.