Southern Garda boat tour lasting 4 hours
DESENZANO -> SIRMIONE -> LAZISE -> BARDOLINO -> GARDA -> PUNTA SAN VIGILIO -> ISOLA DEL GARDA -> DESENZANO
In half a day you can see all the coasts of the lower/southern Garda Lake.
It starts from the port of Desenzano, they ahead for Sirmione could admire the Scaliger Castle and the Caves of Catullus, then continue east until you reach Lazise where you can enjoy the amusement parks. From there, with the bow northwards, skirting Bardolino, Garda and finally Punta San Vigilio where you can horizontally back across the lake and get to circumnavigate Garda Island.
With attention to the steps required to avoid the rocks, you will return to Desenzano along the west coast.