The lakeside promenade in the old town runs along the eastern shore of the peninsula, giving views across the water toward the far shore. It's the standard Sirmione evening walk — olive trees, a low stone wall, families, and the odd boat puttering past.
The best stretch is between the castle and the beginning of the Via Catullo, where the lake is close on both sides of the narrow peninsula. In the evening light, with the mountains reflected in the water, it earns its reputation. Come in the morning if you want it quiet.