The Costa Brava season runs from late April to early October. May, June, and September are the sweet spots — warm enough to swim, not too crowded, the Camí de Ronda walkable without melting. July and August are hot, busy, expensive, and the small beaches fill up by 10 am.
Time it around the Festival de Porta Ferrada (late July to mid-August) for evening concerts in the monastery courtyard — a long-established summer festival drawing jazz, world music, and classical performers, plus occasional theatre.
Winter is mild, quiet, and gloriously empty. Many seafront restaurants close from November to March; the town museums stay open.