The Kim Boi hot springs, in the valley below the Muong hills about 55 km from Hoa Binh city, are among the best-known mineral baths in northern Vietnam. The springs produce alkaline water at around 35–36°C, with a faint sulphur smell but a clean taste — locals drink it as well as bathe in it. Several resorts and bath houses have grown up around the springs; the more modest public pools charge a few dollars entry and are perfectly adequate.
The setting helps: Kim Boi district is a pleasantly green valley, and the springs sit among rice paddies with forested hills rising on either side. For travellers doing the Muong Bi or Giang Mo homestay circuit, a stop at the springs makes a natural finale. The area has become popular enough that weekends bring Vietnamese day-trippers from Hanoi, so midweek visits are calmer.