There are two late-night drinking areas in Venice. Piazza San Marco is not one of them. Although it is very pleasant and there are many people wandering around late. But the actual late night scene is in either Campo Santa Margherita, near the University Ca’ Foscari in Dorsoduro; or in Erbaria on the West side of the Rialto Bridge where the main vegetable market is held during the day.
Although there are many fantastic bars in Venice, if you’re planning a night time “pub crawl” you should plan a few places to visit in advance, otherwise it’s very easy to waste an hour wandering aimlessly in search of a watering hole that’s actually open (especially midweek).
Locals in search of nighttime entertainment mostly head over the bridge into Mestre, or hop the boat to Lido. One exception: F.ta della Misericordia, in Cannaregio (north from the Ghetto over the Ghetto Nuove bridge, turn right), features several bars in succession, anchored by the Paradiso Perduto (Cannaregio 2640; a restaurant by day, live music on Sundays starting at 9), along the canal. In season they are spilling over after dark with youths holding large glasses of rosé, while more of those same youths are cruising (in motor boats) blaring rap songs in Italian from the loudspeakers. The cafes and bars lining the expansive C. Santa Margherita are catering to the students from the nearby university; chill out to reggae sets in Caffé Rosso (Dorsoduro 2963), or dance (Saturdays only) at Round Midnight (Dorsoduro 3102).
Devils Forest Pub. A traditional English style pub with a very fun atmosphere. It is located near the Rialto Bridge and tucked into a small alley near the Disney Store. There are two Irish pubs in Venice. One is located along the Strada Nova in Cannaregio; the other one is the Inishark just before Campo Santa Maria Formosa.