Venice - with St. Mark's Square, the Great Lagoon, the gondolas on the Grand Canal, Venice's Carnival together with great architecture, artistic masterpieces, particular narrow streets, the Biennale, the Marine Republic, but Veneto is not only Venice.
Cortina d'Ampezzo - in the province of Belluno, is part of the Veneto as well. A place with spectacular views of the Dolomites where you can relax and walk in summer and go skiing in winter. The Olympic Wintergames in 1956 helped Cortina d'Ampezzo to become a city known anywhere in the world.
Padova, the ancient and learned city with its Basilica del Santo that houses the relics of Saint Antonio is one of the major attraction points for millions of pilgrims every year.
Lake Garda - the largest italian lake, and a well know tourist destination
Get a map of Venice with the water bus routes. You can see major parts of the city just by getting on and traveling the canals around the major islands.
Just sit in St Marks Square and watch the pigeons, listen to the music, watch the people go by.
The Venetian glass is beautiful.
Be careful about the time of year you go to see Venice. It is under water some times. Planks are put out to walk when the sidewalks are not walkable. If you go the right time of the year, it is a beautiful city and well worth the trip.
Find a website that actually has some information on what to do, not just idle observations and activities that you can do anywhere.