I just really geek out on scope and age of the city. I spent 4 nights there 2 years ago and spent several hours a day just walking around. Lyon and a few other cities have decent sized medieval cores, but they don't compare to the scope of Venice and the wealth the city had to build beautiful. I like Venice in October. Crowds are less and it's not hot. For me, getting lost in Venice and trying to find your way back to where ever you started is one of the most fun things you can do in Europe.