I bought a slackline. If you’re not familiar, a slackline is like a tight-rope, but it’s 2″ wide. In the most simple terms, it’s a 2″ ratchet strap. You can string it up between 2 trees or any other objects that are capable of handling 600 pounds of side-pull. It takes a while to learn, but as you do learn, you get a good core workout. After you’ve learned, then you can start learning tricks. Not like backflips or anything, but things like turning around, squatting, squatting on one leg, sitting and standing back up, etc.
You suspend it about 3 feet above the ground so there’s not a lot of penalty for failure. That means it fits in my wheelhouse.