Mine loves to patrol the tank and look at his reflection. I set up some rock caves on the bottom of his tank (if you want a natural look) just like you would for a bottom dweller, and he loves exploring them.
Just makes sure that anything you put in his tank has no sharp edges, and that all holes are plenty big enough for him to swim through without hurting himself. Bettas will squeeze through impossibly small holes (they're very curious) and tear their fins apart in the process.