Baan Klang Nam, which means House on the Water, is where the locals go, real Thai, hardly any tourists and absolutely buzzing. This isn't a romantic hotspot but it is a great family restaurant. You can even take the mother-in-law if she's tagging along.
A converted teak house right on the Chao Phraya River with a terrific view of the huge Rama IX cable-stayed bridge, all lit up at night. A fun way to get there is by longtail boat from the skytrain pier, right to the dock of the restaurant.
I'd say it's one of Bangkok's best seafood restaurants, really tasty dishes, massive portions, and very helpful waiters. It's good to get away from the super sophisticated Bangkok restaurants and feel the pulse of the city in a place so popular with the people who live there.

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