Want to get the most out of your experience in Piazza San Marco? Museo Correr is a little-known gem on the southern side of the square.
In-the-know tourists come here to buy tickets to the Doge's Palace without a line. One ticket (€16) provides one-time entry to all the St. Mark’s Square Museums: the Doge’s Palace, Museo Correr, Museo Archeologico Nazionale, and the Monumental Rooms of the Biblioteca Nazionale Marciana.
The Museum also provides a stunning overview into the Piazza (as the photo shows).
Lastly (and just as important), the museum is a cool and quiet respite from the crowds in the summer months.
So you're at the Piazza San Marco. You've already done Quadri and Florian, and you know both the crowds and the prices are a bit extreme. But you still want a civilized place to have some coffee, or a dessert, perhaps even a sandwich.
Welcome to the Museum Cafè. It looks out over the Piazza. It has air conditioning. It doesn't require a ticket to the Museum Correr proper (although you should probably stop by, for its collection of art about the city of Venice itself).