We actually met Royal while we were there, and he let us in on some good tips, but there's also a copy of The Ultimate Kauai Guidebook on our coffee table. His place is located near all the major attractions around Princeville. Really easy to come and go from his parking spot.
There are a few boogie boards, goggles and snorkels, and flippers available to use. Royal generously provides enough soap/shampoo/conditioner/towels for a weeklong stay, the other Kaua'ian Airbnbs that we stayed at did not. The limited-use washer/dryer is definitely a plus.
Thank you and we hope to stay again soon!