Here is an illusion in an illusion-- three shadows at the brink of the haha.

Taken just before we left - a freeze frame of a moment. Ha-has, I learned were a device of estate planners to keep livestock from crossing the perimeter of the grounds and into the surrounding countryside -without the visual scar of a fence. Since a ha-ha is recessed rather than raised, the illusion of unrestricted space is maintained.
(Explanation courtesy of my host.)