I have to write this before the thread drops out because everytime i see the thread i think of this - it could be somewhere they tripped and the enclosure was meant to cut the outside world out so they could facilitate an inner trip far more easily and commune with the spirits there, you could sit or even lie on the treetruck, we know this because of seeing those great people sat and laid on it in their failed attempt to save it [from probable churchgoers and archaeologists] and i've sat in a modern version in a sculture park near aberdeen and it is strange how some of your senses are cut off almost straight away.