SW7451 : Valley north of Mithian by redrat
If I recall, this structure is at a place called Blowinghouse in Perran Coombe. (The Grinning Goat of Trevellas was up the hill to the west.) If you walk south from here, then west up a side vale, you'll find Harmony Cot, the birthplace of "The Cornish Wonder", painter John Opie.
I also seem to remember that PEACOCKs dwelt just on the other side of Perran Coombe from this spot. Their loud "coo-WAAH, coo-WAAH" instantly brought to mind the Johnny Weismuller Tarzan movies. Off topic trivia: Many of the outdoor Tarzan scenes were filmed at an estate in Arcadia, California, which is now the Los Angeles County Arboretum. It was home to a flock of decorative peafowl, which called out during the filming of some scenes of Tarzan. Peafowl are native to East Asia. Tarzan was orphaned in Africa.