From the chimney like structure on top and the fireplace looking area at the bottom, I’d guess it’s some kind of hearth i.e. for outdoor cooking. Doesn’t look as if it has been used for a while. I’m not entirely sure why I took this picture. Maybe because I liked the stone and the overall dilapidated, and abandoned look. Or maybe it was because it seemed a little incongruous standing right next to the Old Croton Aqueduct trail (to be honest there was a house nearby so it shouldn’t have seemed out of place).