Once a dilapidated extension of the neighboring KOA campground [1], Bozeman Hot Springs (81123 Gallatin Rd., 406/586-6492, 7 a.m.–10 p.m. Mon.–Thurs., 7 a.m.–sundown Fri., sundown–11 p.m. Sat., 8 a.m.–10 p.m. Sun., $7.50 adult, $6.50 age 5–12, $3.50 age 4 and under) has been refurbished with the addition of a small outdoor pool, several new soaking pools, a sauna, a steam room, a fitness center, and a spa.
The main pool is indoors, in a large room with just a whiff of sulfur in the steamy air, and the atmosphere is homey and family-oriented rather than overly plush.
Links:
[1] http://www.moon.com/destinations/montana/the-missouri-headwaters-and-south-central-montana/bozeman/museums