There are many guidebooks for Kauai and the other islands. Many are good; some not so good. My favorite is Kauai Trailblazer: Where to Hike, Snorkel, Bike, Paddle, Surf. It is available in softcover and e-book at Amazon. The e-book is a little more up to date, with more pictures. I refer to both versions frequently. The book is well organized, directions are precise, and descriptions are accurate. That means pay attention to advice about risks or cautions! Kauai is a great place for outdoor activity but you can get in trouble fast without adequate information or preparation. This book gets you prepared. The book is especially recommended if you plan to extensively hike the island.