Just want to chime in with my experience in Hawaii, specifically relative to tznius and the discussion on what to see/do when you visit a particular place.
I went to Maui for a few days (4 nights) last August. I'm not a huge beach person (or even pool/swimming in general) in the first place, and though my wife very much is, she's less so when it involves an Aqua Modesto, swimming cap, swimming in a skirt, etc. As a result, we didn't really make it a focus in our itinerary. We used the hotel (Fairmont Kea Lani) pools and beach several times, and since I'm pretty nearsighted, I just left my glasses in my room. Would I say I have absolutely no qualms about having done that (or doing it again in the future in Hawaii or elsewhere)? No, definitely not. But I did have some level of comfort that I was taking steps to at least reduce my exposure.
The activities we had planned were RTH, Haleakala sunrise and hiking, and possibly some snorkeling. We tried out snorkeling gear at the hotel, and neither of us were particularly comfortable with it, so we ended up forgoing the snorkeling and doing a hike in Iao Valley State Park. The last (half) day we went back to HNL and did Pearl Harbor. RTH ended up having the most tznius challenges of the bunch, but I pretty much followed the same protocol of taking off my glass when I thought it necessary.
As far going to Hawaii and not hanging out at the beach, snorkeling, etc., having made the trip I would say that if somehow all of the beaches and snorkeling spots were permanently closed and inaccessible, I still would want to go and visit the places I visited. Can you see the type of nature and hiking sights I did elsewhere? Probably something similar, but not the same. I'd argue that there are more places in the world with gorgeous beaches and snorkeling (even if they're not quite as good as Hawaii). It's all a matter of what you want out of your trip. Not having beaches and snorkeling on your activities list shouldn't preclude you from wanting to go to Hawaii.