Going with my sister (two healthy/active 60 year old women)to Venice for the first time in early September and don't really know what to expect. We will have two full days and a half day when we arrive. Where should we start? How should we plan those days? More interested in outdoor sights than in spending hours in museums or galleries. How should we make the most of our time? We will be staying very near the train station in Cannaregio.
Venice is not necessarily an all indoors experience. From your hotel, it's a brisk walk to Piazza San Marco, and if you are up for a more arduous walk, check out the Lido (you'll need to take a ferry part of the way to get there). It's not too late in the season for swimming there and the beach is world class.
But most of all, September is a great time to use Venice as a base while exploring other islands in the lagoon. Burano, for example, is favoured by locals (and me) for it's authentic restaurants (along with less touristy prices).
All of the islands have well preserved architecture and several have ruins from the Roman era. As an additional consideration, take note that during the high season (which encroaches into September), tourists outnumber locals by a mind-numbing 600 to 1! It makes getting away to the outskirts all that more attractive.
You can take ferries or private water taxis to any of the larger islands.