the closest beach to Florence is in Viareggio. you can take the train for about 7 euro and it takes about an hour and a half. go to the trenitalia website to find out train times. you can also take a bus from the Lazzi bus station in Piazza Adua to the right of the S.M.N. train station. you can try http://www.lazzi.it/itanew/activenews.asp for the bus schedule but i'd suggest going to the station itself to check out times.
