Pigeon is a staple in yoga, so you may be familiar with the stretch.

Sit on the ground or a mat and arrange legs as shown in photograph below. One leg is straight behind you, the other is bent at the knee and tucked in front of your body. Gently lean forward over the front leg. Try to sit both butt cheeks down on the ground. Alter the angle you are leaning until you feel a stretch. Hold the stretch for at least 15 seconds on each side, longer if possible.