Rieck's Lake Park sounds like a great smaller alternative to the nearby Merrick State Park. Rieck's Lake also has a (non-reservable) campground. There is plenty of walking, and the park is home to a sheltered picnic area. The playground has your average climber with a couple of slides and a few old-school pieces of equipment as well. Plus, there's a ball diamond!
Rieck's Lake Park
North of Alma on State Highway 35 ~ Alma, WI ~ (608) 685-3330