Paintball is fun, and it's technically a "day off" but man, it's so not a day off - I've never had a harder leg workout than the one and only time I played paintball (I was in the best shape of my life at the time, too). Holy hell, I could barely walk the rest of the day from all the crouch/running.
This is basically a way to say to any naysayers who might think "They should be working out instead!" - trust me, if you've never played, paintball can be a hell of a workout.