I am a little fuzzy on the details - like the mention of no bikes! But this Sunday Piazza Duomo goes pedestrian only. It seems to be quite a big deal - but I wonder what everyone is going to do when they start to lay the tram tracks down (the tram is supposed to come along the north side of the Duomo and turn up Via dei Servi to Piazza San Marco)? Also it is definitely going to change several bus routes. There is a PDF file of the changes here. There will be a free concert Sunday evening in the Duomo as part of the celebration, and the Palazzo Vecchio will also be open until midnight. More details on the schedule of events here.