I drove down the 408 at the coast to see this sight but actually the ONLY thing I really saw was the old town. I tried to stop for others but it was quite crummy, or maybe not obvious enough. I think they are also marked wrong. The island on the lake, Koh Yo(?) is also include I think, but stopping there isn't so easy. You can try to stop on the coast across from Songkhla but again it's not so nice. On the way down from 408 you see LOTS of water basins which is very unusual but as for "water management" I don't quite understand what they are going for.

The MAIN attraction is Songkhla Old Town which can also be reached by plane. It's still open for cars so walking isn't as chilled out as you might expect. You will see a city gate, not as "old" as it should be:

Once past the you can find temples east, docks west, and an old castle wall at the north side.

You can also find many restaurants, some street art a la George Town / Malaka (it's not why this is nominated) and in the evening it gets more relaxed. As mentioned before I didn't see any water management parts here and I think it's not really a reason to nominate. Perhaps there is more in the surrounding areas but hard to find and Songkhla is more of a "center" piece to link these together. It would make more sense to inscribe this was part of an old town but those we also have inscribed way too often. Would it be worthy to visit? Well, no. Main reason is that it's FAR away from the rest of the world. There is an airport but you would have to come here just for Songkhla and not as a fly by. I spent half a day exploring the place and that was enough for sure.