Don't bother if you hate wind and zero cell service, but Luskentyre Beach looks like the Maldives without the heat. Rent a car; public transport here is basically a suggestion. Spend at least two days driving the single-track roads to find the best spots. Skip the overpriced souvenirs and grab a drink at the Harris Distillery instead. Pack a raincoat because the weather changes every ten minutes. It is just you, sheep, and endless Atlantic views.
