If I stick to the rule «the length of the beach description is equal to the length of the beach», then the whole post would fit into a word «Ao». Seriously, there's even a definition «Beach» not entirely appropriate, because I would call it just a beautiful place for selfies, or, at most, for snorkeling. There is no sand here, even conditional, even coarse, even with garbage.
The coast consists of pebbles of different sizes (in the sense of stones, not nudists), which is very difficult to walk along without stumbling. And it is quite possible to break your legs and ribs on green stones under water - very slippery from mud.
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I recommend keeping Ao Hin Ngam in mind as a pleasant stopover when traveling between real beaches. The bay is located at the bottom of a decent cliff, to which a capitally constructed concrete staircase with railings descends. The bike can be parked in the microscopic parking lot at the beginning of the stairs, go down and sit in seclusion for a while.
It will be better if you take a packet of Thai snacks with you, so the time will pass more interestingly and with benefit. The sea view here is oriented to the northeast, but due to the peculiar geography in this part of Phangan, you will not be able to see the sunrise or sunset.
Entering the water only on stones and only on four limbs, and try to get into a buoyant state as soon as possible, the depth will be 15-20 meters during high tide. Then the bottom goes down sharply and you will have the opportunity to snorkel more or less bearable for local waters. Waves are present, on windy days it is better to come purely for contemplation, to swim is dangerous.
There is a good concrete road all the way to the bay and there is a normal parking place. A capital sala has been built near the parking lot, in which you can comfortably wait out the rain or have a snack with takevey. As for shops, houses and attractions - directly on the very Ao Hin Ngam there is none of the above. Not far from the stairs there is a small resort on the slopes of the mountain, you can see it in the last picture. I didn't know the prices, it's called Baan Moonsiri @Hin Ngam. You won't have to search for the beach, I marked it on the map with a marker.
Ao Hin Ngam Beach Map
Ao Hin Ngam Beach Map: