Slides in an adult playground? Absolutely. Not only is sliding down one a lot of fun -- and isn't that the point of being at an adult playground? -- every time you climb back up for another ride, you're giving your calves a good workout, whether you climb the ladder or walk up the slide itself.
While you climb, be aware of your arms: For the best lower body climbing workout and balance training don't pull yourself up by or lean on your arms as you climb -- you want your leg and core muscles (that's your abs, pelvis, hips and back) to do the work.