If you're in Honolulu and want to go snorkeling then Hanauma Bay is a must. The water is clear and there are plenty of fish. I went with my family of 6. We had never snorkeled before and we loved it. We had only planned to stay 2 or 3 hours but ended up staying half the day. This was one of our favorite things we did in Hawaii.
Go early as it gets crowded as the day goes on. There is a snorkel rental place right on the beach. Take water and snacks as there isn't anywhere to buy food on the beach. You have to walk back up the long steep hill to get food.
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