Glorious Venice and its lagoon are the focal points of Po River itineraries, with voyages only traveling as far upriver as Polesella, then returning to the city that’s nicknamed La Serenissima. Just two major lines venture onto the Po, Uniworld and CroisiEurope, with trips that run seven to 15 days; longer tours add land-based segments to Milan, Florence, and Rome. European Waterways has 20-passenger barge trips that go about 60 miles further, to Mantua. Cruise season runs from the end of March to the beginning of November, with late spring and early fall being the most pleasant times to travel. November presents more risk of flood tides in Venice.