Sounds like a great experience. I loved Orkney, will definitely be going back.
Different, but the same in many ways, I went up to Castlerigg in (very) thick fog one night a couple of years ago and I will never forget that experience. Complete silence and a grey shroud over everything. It was both frightening and thrilling, the sense of there being 'something' (I don't know what) there was so strong, and together with the knowledge, or imaginings of what took place there, it got all bit much!