Your core isn't just there to look good at the beach. That's what rotational training is for. A cable core rotation (or band version at home) works the muscles responsible for twisting, bracing, and resisting force from the side. Reaching across your body, picking something up off the floor at an angle, any sport that involves a swing or a throw or a change of direction. Your core is involved in all of it. Most people train abs with crunches and call it covered. But if you're skipping rotation,

The Earth's Core: Secrets of the Inner and Outer Layers Explained