Preservation efforts around Hanauma Bay limit the number of tourists allowed in at any given time, however if you arrive early enough you shouldn't have a problem getting in. We booked our trip with a tour operator who shuttled us from our hotel to Hanauma Bay and provided us with all of our snorkeling gear - mask, snorkel, flippers, and vest.
Some of the brief footage I shot underwater at Hanauma Bay.
I've never snorkeled outside of a swimming pool before, but I had no problem picking it up pretty quickly in the calm waters of Hanauma Bay. The views above the reef were amazing and I saw all kinds of colorful fish and corals. I even bought a waterproof case for my phone so that I could shoot some pictures underwater.
It's one of those activities that you can't really capture the sensation as you experience it, but I did come away with some nice shots. In total we spent about 4 hours at Hanauma Bay and that proved to be more than enough time to see and do everything we wanted to there. As far as things to do in a tropical locale are concerned, this is a must.