It took some searching before I found any info on this structure. It about the size of a small room and the only opening is now blocked with the concrete barricades that you can see in the photo. It’s a fireplace! An earlier picture I found shows that you could walk inside and there are actually 2 fireplaces inside. I imagine it was used by visitors who came to the Parklands to use a beach that was once here, to picnic, to hike the many trails. There's also a nearby pond and railroad tracks. The area once had a thriving business harvesting ice from the pond and transported it by train to nearby towns.