This Knee-to-Chest Stretch is one of the best lower back stretches because you can work one side at a time. Plus, lying on your back is so relaxing, and it's just what you need after a vigorous day on the mountain.
Lie on your back, pressing your lower spine into the floor. Bend your right knee and hug it into your chest. Hold here for thirty seconds. Cross your right knee over to the left and turn your head to the right for a nice twist, holding for another thirty seconds. The release and repeat on the left side.