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When the road to Haad Kho Khao hits the beach, head to the right to find ten foodstalls all serving inexpensive dishes of Isaan food and grilled seafood. The usual fare of yam spicy salads, laab, som tam, dtom yam and sticky rice is all pretty standard, but it's a nicely basic and untouristy location. Every restaurant has a somewhat ramshackle bamboo sala or two, protecting the wooden benches or the faux-wood concrete tables and chairs, and if the atmosphere isn't added to by a party of locals with a guitar, there's a knackered old jukebox that plays Thai music to accompany your meal.
It's a nice place to get away from it all for a while, and if you want to make an afternoon of it, get a bottle of something with a bucket of ice and grab a selection of dishes off the menu. The beach isn't really great for sunbathing so it's best not to come with that idea, and the gravel works across the way doesn't make it the prettiest of pictures. But if you haven't made it to somewhere that offers proper Thai food before, this would be a good place to try first.