We did a day trip here by renting a car from Enterprise at Discovery Bay Centre, Waikiki (best prices thru Costco, great service) and it's worth the drive away from the big city. Favourite places to go were Laniakea Beach for spotting sea turtles and Haleiwa Beach Park for parking, playground, basketball court, green areas for shade and picnicking, and access to surf-watching/ lessons. Great lunch at Kahuku Farms. Should snorkel here to avoid the crowds at Hanauma Bay. If you have a week to stay on the Island, you should try to venture to North Shore if you want to get away from the madding crowd of Honolulu and the southern coast.