Looking to work on your core? Try the Captain's Chair leg raises at your gym. Repeat this for 4 sets of 15 each. Try to keep your upper body straight and grip the handle bars as you do this so that all the power to lift your legs is coming from your core.
The video shows this exercise with straight legs lifted, but you can also try this with knees lifted towards the chest.
Cheers Eights & Weights!