There is a large, mountainous island off the coast of County Mayo called Achill. If you ignore all the tourist/golf course junk at that link, there is a lot of interesting information to be found there. Could this be the ancient home of our fictitious or semi-fictitious Aracos clan? The "Hawk of Achill" in myth and folklore is supposed to be the oldest living creature with memories of everything that happened before history was recorded, some of which is preserved in a dialog between the Hawk and Fintan mac Bochna. (I have the English translation if anyone is interested.) I don't know who originally created the idea of the Aracos clan but in reading over the archives of Crannog Niall, I always imagined them as coming from Achill.