Fintan,
Not so sure about Northern Ireland (currently doing research) but if you are in/around Donegal, I would recommend heading toward Dunlewey (
http://www.dunleweycentre.com/index.htm) it's about 10 years since I was there but my recollection is that there is some spectacular scenery along the route to get to Dulewey. This is not seascape location but worth a look.
David