Over past the end of the field through the woods for a little ways (just before the terrain drops away steeply) there was a very large  boulder that protruded from the ground in such a way that it sheltered a pretty good size area.  Someone had meticulously built stonewalls to enclose the area underneath and Jimmy called this Donald's Indian Cave.  There was a nifty arch built into one of the stone walls making a small doorway, even as a child I had to hunch down quite low to get through (it was much easier to climb over the walls as they were only about 4 feet tall or so).  I bet I could find this location quite easily as I spent so much time outdoors there.