From reader Joe:
The attached photos were taken in some woods just beyond the property of my boss in Shutesbury, MA. Perhaps they are of interest to you.
...I'm desperate to find out what this structure is, but we can't have all sorts of strangers just walking into someone else's private property, potentially disturbing this site. Which, may have already happened as my boss told me this structure once had a capstone on top, and there may be photos from decades ago which show that. I'm on the hunt to find some of those photos. Perhaps the flat stone on the ground in front of the opening of the stone structure was once that capstone?[PWAX: I was going to write that I have seen a few things like this. One in Groton got reported a couple times but I cannot find it to link to. However, I see this structure has a bit of a "tail" on one side and some other complexities that make this structure unique.]