This hot springs is hands down my favorite. I've returned to Lolo every time I'm back in MT. Even though the hot springs has a concrete building surrounding it, it is great! The actual hot springs is enclosed with an opening at the top, allowing for some airflow. The outdoor pool is a pretty good size and there are showers and changing rooms near the front desk.
My favorite thing is to alternate, the springs, pool, and snow. It feels amazing. The restaurant is good too. The menu is very decent and the food is tasty. I would recommend visiting.