Venice is a truly unique and beautiful city to visit. You can wander aimlessly around following the canals, soaking up the architecture and eating a Gelato (or two). If you can afford it- a Gondola ride.
It doesn’t matter how much time you choose to spend in Venice- Two days could be spent wandering the magnificent canals, or you could visit for a few hours by train and still see most of the beautiful sights that Venice has to offer. One thing I recommend is just get lost. Loose the map and put away the iPhone- just wander and you will stumble across the back canals and residential areas which give you a proper insight to how the Venetians live.
Some of the main attractions not to be missed are:
The Grand Canal
St. Marks Square
St. Marks Basicalla