The Rossini Opera Festival runs for three weeks each August and is the main reason to plan a visit around a specific date. Tickets sell out months in advance for the major productions, though the festival also hosts concerts and free outdoor events. The city is lively and at its most festive during the festival, though accommodation gets expensive and scarce.
Spring (April–June) and early autumn (September–October) are the most comfortable times for sightseeing — warm, uncrowded, and with full access to the beaches without the high-season crush. The Adriatic is swimmable from June through September. Winter is quiet; most of the city's cultural institutions stay open, and you can have the Musei Civici to yourself.