We did a luau in Kauai (my favorite island) that was great. It was through the cruise line. Probably $10 higher than booking it on your own, but it was exclusively for cruise ship passengers only, and transportation included to and from the ship was convenient. We have done a luau before, privately, and it was okay as well, but this one seemed to be a higher quality luau, as was the food served.
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Norwegian Cruise Line