Head north out of Stanley on Hwy 75 and about 12 miles on you'll find one of the most popular hot springs in the region. The water is piped under the highway and flows into rock pools created by bathers over the years. The source water is extremely hot - as high as 160 degrees - and the rocks can moved to create pools of different temperatures. Use of the springs is free, restroom facilities are available, and the original bathhouse, built in 1937 by the CCC, is preserved as a historic tribute to their craftsmanship.
If you go:
The easy accessibility of the springs - the Salmon River is right next to the highway - means the pools are often packed with bathers in summer. The proximity to the highway means bathing suits are necessary.
Links:

Idaho 75
Stanley, Idaho 83278 USA
information@stanleycc.org
Mailing address:
Stanley-Sawtooth Chamber of Commerce
PO Box 8,
Stanley, ID 83278 USA
Phone Numbers:
Stanley-Sawtooth Chamber of Commerce
+1 (208) 774-3411
+1 (208) 774-3411
Toll free
+1 (800) 878-7950
+1 (800) 878-7950