Totally agree with Ocifant re. Boscowen Un. I would add that Kennidjack is a really atmospheric natural featur, with a nice little stone circle set below - I had a very strange experience there.
I think some cool bloke that used to be in a very cool new wave band, and did lots of cool/fried solo stuff wrote a big book about all of these - can't think of his name ........=;o)