Though the resort we stayed at on Oahu was in Waikiki (as are 100 of the 104 Oahu resorts), we spent a fair portion of our time on the island exploring areas beyond the crowded beach. Our wanderings were facilitated by an amazing book called Oahu Revealed. This book was recommended to us by almost every past Hawaii traveler, and for good reason. As long as you ignore the food recommendations (their inclusion of chain restaurants made me bonkers - does a travel guidebook really need to print a review of a restaurant that is ubiquitous in every US suburb?), it gives you a real local point of view on the sights and sounds of the islands. I really felt like we were seeing things that other tour books might not have included.
Anyway,Turtle Beach is NOT one of those things, as I'm quite sure it's included in every Oahu tour book under the sun. How could it not be? The non-descript beach is positively swarming with Green Sea Turtles. It's truly remarkable. Located halfway between Waimea and Hale'iwa right off of 83, it can be kind of hard to find, as there aren't any giant signs. We realized we had arrived because of the sheer number of cars parked on the side of the road. Oh, and then I glanced over to the water (about a 100 feet away) and literally saw the turtles from my car window.
After you park, cross the street and carefully make your way down to the beach (it can be kind of hard to find a good place to get down). The turtles are usually swimming everywhere, but when they crawl onto the sand, you'll spot a red rope surrounding them with some volunteers sitting guard.