Do you remember how good it felt to play on the swings, your legs above the ground and your hair blowing in the wind? Odds are, you'll feel the same way now that you're an adult, but all that fun comes with a bonus. While you feel free as a bird, you'll also be working out your arms and abs as you glide through the air -- and if you swing for about 20 minutes, you'll burn about 100 calories [source: Self].
The swing set can also be used for more traditional strength training. Try holding on to the seat while you hold a plank pose, or try keeping your balance doing knee lifts while you stand on the seat to change things up.