If you feed pellets then a treat ball is good fun and good exercise. Mine aren't giant rabbits but I found they managed to break the rabbit treat balls quite quickly so now they have dog treat balls instead. You want the hard plastic types rather than the rubbery ones and as they are designed for rottweilers they should stand up to even a giant rabbit.
If you only have one rabbit you may like to consider getting a second rabbit, you'll find lots of advice about bonding on this forum.