The water village of Zhouzhuang sits about 30km southeast of Suzhou and is the most visited of the ancient canal towns in the Yangtze Delta region. It's commercialised — entrance tickets, souvenir stalls, tour groups — but the old stone bridges and canal streets are still intact and genuinely atmospheric, especially early in the morning before the day-trippers arrive. Zhouzhuang is also a reasonable stop on the way between Suzhou and Shanghai rather than a dedicated detour.
Tongli, a smaller water village about 20km south of Suzhou, is quieter and less polished than Zhouzhuang. The canals are narrower, the crowds thinner, and the pace slower. Worth it if you have time for one water village and want to avoid the larger tour groups.
Taihu Lake, China's third-largest freshwater lake, lies about 20km west of the city. The lakeside is popular with local day-trippers, and boat trips to the islands are available from several docking points. The scenery is pleasant rather than spectacular, but the lake produces the freshwater crabs and Biluochun tea that Suzhou is known for.