Venice in January.
I was in Venice on 31th of December, and Jan 1st. I anticipated the atmosphere, joyful, romantic one. But... there's no special event in the city. I should have stayed in Barcelona. It's Pity. However, It is one of the most beautiful cities, and you should come once in your lifetime. I recommend not to stay your whole time in the main island. Other islands have value to visit, also.