Venice rewards visitors who avoid the obvious. Summer is the worst time to come — heat, mosquitoes, the sticky smell of low water in the side canals, and crowds so thick that the alleys around San Marco become single-file. The exceptions are the Biennale (the international art exhibition that runs from May to November in odd years and the architecture biennale in even years) and the Festa del Redentore on the third Sunday of July, when the city stages an enormous fireworks show across the Bacino and locals watch from boats.
October to early November is the sweet spot — crisp air, manageable crowds, and the start of the autumn light that flatters the city's faded palaces. Acqua alta, the seasonal high tides that flood low-lying parts of the city, begin in October; the city lays out elevated walkways and the floods generally last only a few hours.
Winter can be foggy, damp and quietly magical, with hardly a tourist in sight — except during the two weeks of Carnevale before Lent, when the city explodes back into masked, costumed extravagance. Spring is mild and lovely; aperitivo on an outdoor terrace is one of the great Venetian pleasures. The Vogalonga rowing regatta in mid-May draws over 400 boats from clubs across the lagoon and beyond — a less commercial alternative to the historical regattas later in the year.