A few miles from Honolulu you can find yourself at Tracks Beach, a white sand beach with crystal blue water and almost no one around. Bring your beach toys, and a picnic and enjoy the restful side of the island of Oahu.
Coming from Honolulu you'll take the H1 West to the 93 West and just stay on that the whole way until you see the turnoff on your left. From the North Shore, it's a little more complicated, but take the 83 West to the 99 South, jump on the H2 South, then the H1 West to the 93 West (clicking on the directions from the map on here is probably your best best).
Once you get here there isn't much, which is the best part. There is a small little dirt parking lot for about 20 cars or so. But from here you can walk half a mile in any direction and see nothing but blue skies, bluer ocean and fine white sand. The locals are super friendly, people sometimes snorkel on the south end of the beach at a place called Electric Beach (since it's in front of a power plant) and the vibe is just SUPER laid back and relaxing. You can pick up some food and drinks in town and make this a great day trip or just a nice relaxing few hours on the way to or from Honolulu.
Again, just let everything go and enjoy this slice of paradise.