One of the finest of the water towns within easy day-trip range of Shanghai or Suzhou, Zhouzhuang (Zhōuzhuāng, 周庄) boasts a stock of Ming, Qing and even Yuan Dynasty buildings that comprise some 60% of its total architectural heritage. Willow-lined canals flow past houses with whitewashed walls shaded by grey-slated roofs and carved, curving wooden eaves. From the right vantage points, the view isn't all that different from what Marco Polo might have seen on his visits to this part of China.
A small place, Zhouzhuang is worth a leisurely day of strolling over its historic arched bridges like the Twin Bridges, its cobbled lanes, taking a boat tour of the canals (RMB 100 or RMB 150 for the Shen Wansan boat tour) and visiting centuries-old treasures like the merchant villas the Zhang Residence and Shen Residence; Quanfu Buddhist Temple; South Lake Garden (Nán Hú Yuán, 南湖园); and Chengxu Temple. There's also a fine museum featuring examples of traditional regional crafts and fishing implements.
Note that entry to the town, including most attractions, is RMB 100 for the day (or RMB 80 after 4pm). If you plan to spend a couple of days make sure to tell the ticket vendor who will direct you to an office to get a scan. They'll sit you down and take your picture, which will be printed on the ticket for verification the next day.