Side Split (sometimes called the Front Split or Hanuman's Pose in Yoga) is advanced posture demands very flexible hamstrings and hip flexors. If you don't quite have your full splits yet, just get to the deepest range of motion you are capable of without pain and hold there. Make sure you are thoroughly warmed up before trying this.
Tutorial (1-10 min)
Squat / Lunge Seated
Lower Body Hamstrings Hip Flexors