Although, I have only been to Venice for literally half a day, having taken a bus ride from a small ski town in the south of Switzerland, (didn’t know you could do that!) The main area when you get off the ferry, St Mark’s Square is awe inspiring. St Marks Basilica demands reverence with its enormous presence.
Buy a bag of bird feed and be swarmed by pidgeons who know exactly what you’re up to. Sit along one of the many cafes lines with thousands of chairs for people watching, which is always fun.