Thunderbolt Pose (Vajrasana)

Kneel and sit back on your heels with the tops of your feet in contact with the floor. Your soles will stretch and curve into a good arch underneath you. Keep your big toes and heels together so there is no gap or space between the feet. If the front of your ankles are not flexible enough to rest comfortably on the floor without a space, use a small towel rolled into a tight tube shape to place underneath, and gradually use smaller cloths until you no longer need this prop.
Sit with your back and spine straight but not tense. Let your spine lengthen upward without forcing it. Imagine a string attached to the top of your head up to a bunch of helium balloons. On your breath inhale relax and balance, then on the exhale allow your spine to lengthen and straighten, stretching gently upward.
Aim to stay in this position for 5 minutes. If this is uncomfortable or you experience "pins and needles," you probably need a larger rolled towel beneath the front of your ankles.