Upper Potosi Hot Springs is a 1.7 mile lightly trafficked out and back trail located near Pony, Montana that features hot springs and is good for all skill levels. The trail is primarily used for hiking and walking and is accessible from June until September.
This hot springs is back by Potosi campground. I hiked the trail at midnight a few days ago (end of May). The trail was easy to follow and pretty easy, I'm sure very easy in the daylight. It was amazing at night. We had the spring to ourselves and sat in the dark with a crystal clear night sky. Amazing star gazing opportunity. If you don't have a vehicle with access to cross the creek, you'll have to walk across. We did this late at night and it was pretty cold, but manageable. Be careful! Also, you are in MT, bring some bear spray.
Trail goes by hot pots on the way to a reservoir accessible by 4wheeler