Lower left abdominal pain radiating to the back, what is there?

Many body parts... The left lower abdomen has muscles of the abdominal wall (and the nerves coming out of the spinal cord, going to the muscles), part of the large intestine (colon), the ureter from the left kidney to the bladder, part of the small intestine, the left ovary (lower down), etc... Pain can come from a variety of problems, so anything other than mild brief pain should be evaluated by a doctor.