Shimin no Mori is a peaceful place to take a break. Have a picnic, toss a ball around or just lie on the grass and close your eyes for a while.
You'll find Shimin no Mori in the large ward of Kita Ward. Entry here is free, so you can leave your credit card safely in your bag. While you're in the area, why not check out a few other great sights, such as Saitama Stadium 2002, Omiya Park and Hikawa Shrine?