Swim Under A Waterfall
While Oahu is famous for Waikiki, which was once a playground for Hawaiian royalty, there are plenty of quieter spots away from the crowd. Pack a picnic and take a stroll down the Manoa Falls Trail. After about a mile, the trail opens up to reveal a sparkling white waterfall and freshwater pool. While the spot isn't exactly a secret, it's likely to be less crowded than some of the Waikiki beaches.