70 miles (110 km) from Sapa sits a town that you should not miss, Bac Ha. In this town takes place another famous local market every sunday. This market is less touristy than the market in Sapa.
In the market of Bac Ha you will have the chance to see more ethnic minority groups than in Sapa, but the infrastructure is not as good. For this reason I recommend staying in Sapa, and leaving early in the morning. You can get to Bac Ha on a mini bus or on a 4 wheeled vehicle from Sapa. Many of the tours that you can reserve in Hanoi offer the possibility to visit the two towns and their markets.