If you don't mind a little drive, there's a hot spring you may not have heard of north of Twin Falls.

This one is off the beaten path, but might be worth the trip if you don't mind a little adventure. It's called Goldbug Hot Spring and it's a mild 4 hour trip to the north.

Twin Falls to Goldbug Hot Spring, Google Maps

Whether or not this is worth your gas depends on what you're looking for. The size of the hot spring is not substantial. However, the mountain view is hard to beat.

After watching the video of the group that found this, my only concern is one comment they made on the path that leads to Goldbug. "The bathroom smells like broccoli". That's not a good thing.

If you can get past the broccoli smell near the restroom, Goldbug Hot Spring might be worth checking out.