Yes, Ankor Wat is a must see. Take at least 2 days
Agreed, you need two days plus. If you get enough of the ruins have your guide drive you to the northern-most part of Tonle Sap (which is a massive lake). There used to be prmitive communities of houseboat dwellers on the lake, that were truly remarkable.*
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*This was five years ago, but I doubt the modern world has found its way to Tonle Sap yet.