Continued from yesterday ...

It was a religious plaque. Then to my amazement, I noticed high up in the trees dozens of them, some 60 ft plus in the air and grown into the bows. I subsequently checked the growth rate of those trees and established that they must have been placed there at least 80 years ago if not more. This revelation led to the real mystery. A large circular steel door not unlike those you'd see on a German U-boat, set into the side of the dell head. 
I later questioned the owner who told me that she and her husband had purchased the property in the 1960's from another couple who'd had it since the 1910's, and that in all that time, none of them had known why it was there, who put it there and for what purpose, and none of them had ever opened the door for fear of what may be released from behind it. 

I just had to write a novel about that, and it will be released on March 21st!