Älvsjöbadet bath

Pool baths outside, https://motionera.stockholm/hitta-utomhusbassang/utomhusbassang/alvsjobadet/ for opening hours.
Around the pool area is the large open grass surfaces. Here you will find a good place for your blanket and whatever you have brought with you. If you want to grill, you'll be fine if you do this at the barbecue. If your legs feel tense, there are nice walking paths to walk, or you roll out a ball and invite you to a football game.