What to Do on Fakarava & Nuku Hiva

I will be on a cruise that stops at Fakarava and Nuku Hiva for a day at each, but l can’t seem to find tours or activities to do there.

Could anyone please advise if they have been to either island and found amazing things to do there. Or is it just a place to swim and snorkel? Are there shops and markets or perhaps an activity for the cruise ship visit?