The red "X" marks the location of a curious enclosure in the Littleton, MA Town Forest.
I could not photo it very well but this shows the view, from the water side, of an area enclosed by stone walls with only a single opening in the direction of the swamp:Here is the opening, looking out:The plan was something like this:The enclosure was maybe 70 feet across and seemed to be full of large tumbled boulders. What could this be for? Maybe this video gives a glimpse of the place:
There was a standing stone, fifty yards away in the woods in one direction:There were a few very minor rock structures across the water about 20 yards from the enclosure:I do not know if this enclosure is unique. I can't come up with any guesses as to its purpose. Have you seen anything like this?