The Riva degli Schiavoni is definitely something to see in Venice in two days: it is a sort of monumental promenade of Venice, which extends from Piazza San Marco and follows the trend of the San Marco basin. The whole wide street is adorned with stalls and various monuments, but what I suggest you do is simply enjoy a nice walk while admiring the view of the island of San Giorgio, the passing boats and the profile of the majestic buildings of Venice in distance.