Reddit reviews The Ultimate Kauai Guidebook: Kauai Revealed

Dude, I'm gonna hook you up. Kauai (one of the Hawaiian islands) is where you need to go. Its where they filmed Jurassic Park--so you know the kind of scenery to expect. None of the buildings on the island are over 3 stories tall (by law I think). There's tons of nature stuff to experience: hiking, scuba, snorkel, surf, waterfalls to jump off of. My wife and I went on our honeymoon. We had a blast. We rented this place for the week. We used this guide book and didn't spend a dime on activities. Use Kayak to book your flight. You will have to rent a car. I suggest you get a jeep, because there's an awesome beach on the west side of the island that you have to drive off-road to get to.

Rented the place for a week, got groceries, snorkel gear, car rental, etc and you've got a great time for under $2,000 +airfare.

Ask the natives / hotel desk guy about the Queens Bath and head there in the afternoon. There is a ton of hiking and other fun free stuff pretty much anywhere you go. If there is a full moon or close enough get yourself to a beach that has a good clear view of it and show up at midnight, it'll be just like dusk on a normal clear night, wicked bright.

Also check out this book, has every fun thing imaginable. I've spent about for weeks there on various trips and every time I find something new.

http://www.amazon.com/Ultimate-Kauai-Guidebook-Revealed/dp/0971727953