JazzAscona is the town's best-known event, a summer festival that fills the lakefront and nearby streets with New Orleans jazz, swing, blues, and small-stage concerts. It suits Ascona well: music spills out into a place already built for evening wandering.
If you are choosing when to visit, the festival is a real reason to time the trip. Book early, expect busier restaurants and ferries, and leave room for the pleasure of hearing a brass band drift across the water after dinner.