Blackbird Hall is located on Orkney Islands in the north of Scotland. Orkney was a very special place not only in The Flight of Gemma Hardy, being the home of Mr. Sinclair, but in the lore of Scotland as a nation. Orkney is supposedly the home of such literary giants as Sir Gareth, Sir Gaheris, Sir Gawaine, and Sir Agravain in the Arthurian Legends. Orkney is specifically important in the 1960s-1980s, because of the potitential for uranuim mines, which were never formed, helping to keep the islands as natural and Gothic as always. 

(https://www.express.co.uk/comment/columnists/john-ingham/940355/orkney-islands-best-place-to-live-in-britain-survey-result-comment)