Sirmione sits on a narrow peninsula on the southern shore of Lake Garda, about 10 km west of the A4 Milan–Venice motorway (exit Sirmione/Desenzano). By road from Milan it's around an hour; from Verona, about 40 minutes.
There is no train station in Sirmione itself. The nearest is Desenzano del Garda, about 9 km away, on the main Milan–Venice line. From Desenzano there are buses to Sirmione (Linea 15, operated by Arriva/APAM), or taxis. Verona Porta Nuova station is slightly further but is a major rail hub with better connections.
Once in Sirmione, cars must be left in the car parks outside the old town — the peninsular road is closed to non-resident vehicles. In peak season, even the car parks fill early. Arriving by bus avoids this entirely.