Fans of the building, bought 50 years ago for £20,000, are told to expect a "big surprise".
The aerial images show an immaculate and expansive private garden that is being left to a charity.
Owners who have created and tended a 32-acre garden over 50 years, leave their "legacy" to charity.
Six Mile House drainage mill was "pretty hollow" before the apprentices set to work on it.
