Ao Kao is the longest and most developed beach on Koh Mak, running along the south-west of the island. A few low-key resorts back the sand, but the beach itself stays uncrowded even in high season. The water is shallow and calm — wading distance for fifty metres — which makes it good for families.
At low tide the exposed reef south of the beach is a decent snorkel; at sunset there is a clear view across to Koh Kham and the smaller islets offshore. Several beach bars stay open into the evening for the very modest version of nightlife the island offers.