Years ago when I visited Ireland we came across a field of "mini-dolmens" looking sort of like this.
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/../
We didn't have anyone to ask and I have often wondered if they were a joke or an art piece or someones hobby. Each one was about 12 - 18 inches high. For a moment I thought your photo was the same but in my field they were all three parters, two walls and a roof. Any ideas out there? campground for the wee folk??

edit. Ha it worked. It's really hard to draw when the finished post isn't the same shape as the page you draw on