Ashtanga Yoga Baddakonasana / Baddha Konasana
This is one of my favorite Asana, it is beneficial during menstruation and pregnancy. It relieves stiffness in ankles, knees and hips, prevents varicose veins, and prepares the body for sitting in meditation.
If you would like to try a variation you can lay on your back, with you bottom touching the wall and your feet raised vertically, leaning against the wall. From there allow your knees to bend sideways and let the bottom of your feet touch. You hopefully are now in an upside down version of standard Baddhakonasana. This is very relaxing for your body and lets you stretch gently.