Barra Airport is the world's only airport where scheduled flights land on a beach. The three runways are marked by poles and are usable only when the tide is out — at high tide, the runway is under water. Loganair operates twice-daily flights from Glasgow using Twin Otter prop planes. You can watch arrivals from the dunes above the beach, standing perhaps twenty metres from the touchdown point.
The airport closes when the tide does not cooperate, which gives Barra a charmingly fatalistic approach to air travel. If you are flying in or out, allow flexibility in your onward plans.