there are more than a few beaches up north, and most are quiet with not many pedestrians/sunbathers, Thurso, Dornoch, Nairn etc, though i would recommend Thurso, just a few miles out of town there is a lovely beach at dunnet bay, ideal for surfing, kiting, buggy etc, also there is plenty of pubs to keep warm in at night,
the locals are friendly, the scenery is cool, the only problem is, its at the far north of scotland and the midges are vicious