Nearly everyone comes for the Amphawa Floating Market, opened on weekends only. It gives an impression of the canalside way of live, where farmers in traditional clothing sell their produce. Unlike Damnoen Saduak, this is an afternoon market, so you can easily combine the two into a single trip. It starts to get going around noon, but is at its best around 15:00.
There are also several historical attractions close to here. For details see the Samut Songkhram page - the market is within this Province.