LOL - nice ideas, but a little too technical for the truth!! It's actually a disused Lime Kiln - approx 8 foot across - I was in the chambers underneath which have little access holes. Poked the camera through and took the pic, forgetting the forced flash was on from a previous shot.... The weeds were obviously on a little 'shelf' and the grass around the top is where it's overgrown through disuse. This is it from above...... P.S. - Good idea, BSteph - I had the tripod with me, I should have used the timer on he camera and pushed it further in to get a shot from nearer the middle!! Thanks, mate, I'll remember that for the future.....