Land Mines are an incredible exercise that work your core including your obliques.
Stand with feet shoulder-width apart and grasp a bar that is anchored to the floor on the opposite end.
You can perform this with no weight on the bar or add plates for increased difficulty.
Lift the bar to your chest and begin to rotate from left to right and then back again. Keep your lower body still, you are rotating from the hips upward.
The key to this is two-fold. You want to make sure that you are fully twisting to each side (NO half twists!) and also don't rush the movement. Use smooth, slow, and fluid movements.