Waikiki Beach. Sand, salt, an abundance of palm trees and people of all shapes and sizes basking in the ever present sunshine.
If you are coming to Oahu you will come to the famous Waikiki Beach, it is a given. It is very popular with tourists from all walks of life. You'll get your beach babes, your sun kissed gods and goddesses, your mums and dads and your grannies and grandpas and yes... The children... Who run over your beach mats and have a wild time.
Prime beach real estate is an issue here. If you're the kind of person who likes to sprawl out and have your space around you... It isn't going to happen. Being so popular at all times of day, the beach will always be packed. Great if you love to people watch and mingle and make new friends, not so great if you are looking for quiet and relaxing times.
Don't get me wrong, it is absolutely beautiful here... The water is always at a perfect temperature, the sand is soft, you can catch a glimpse of two of cute turtles frolicking in the waves... But it is extremely crowded which can get quite frustrating when you just want to plonk your goodies down, strip off and nail it for the water and come out to sprawl like there is no tomorrow.
Your best bet at finding a good spot is to stick to the outskirts or have a wander down the beach towards the resorts... There are some designated spots where you can rent a beach lounge and umbrella and hang out all day... However that's not entirely necessary. Just head away from the main drag and you'll get some space with the same view and the same awesome beach... Just a few less people to kick sand in your eyes as they barge each other across the crowded beach.
If you're adventurous, you can hire surfboards and or paddle boards (my advice is don't hire off people at the beach... You can get pretty good deals a street behind the main drag and the beach merchants will rip you off)
Go snorkeling... But maybe bring your own gear if you can fit it as they charge tourists through the teeth over here for this sort of thing. Just go pick up a cheap snorkel set at home and pop it in your suitcase. Guarantee you will see turtles and other beautiful sea creatures not too far from the shore.
Over all, a must see / do. I mean come on... it's Waikiki Beach!!