Piran's town beaches are small and rocky — the peninsula itself doesn't have much sand. The best swimming is at Fiesa, a small bay about a 20-minute walk around the headland from the old town, with two calm coves and a handful of beach bars. Portorož, a short bus ride south, has longer sandy beaches and the full resort infrastructure if you want sunbeds and water sports. Most people make day trips there from Piran rather than the other way around.