We rented two little mopeds for the day and scooted east along the coast to Hanauma Bay Nature Preserve, "a wide, curved bay of sapphire and turquoise waters protected by a rugged volcanic ring". We rented snorkeling gear and swam through the shallow reefs just off the shore. The coral was a bit meagre, but we saw lots of brightly-colored fish which weren't bothered by us at all.
After some good snorkeling and sun, we scooted back along the coast, and then north up to Manoa Falls. We squelched our way along a very muddy trail beside the Waihi Stream through a rain forest to the idyllic little waterfall at the end.
Renting the scooters was a great way to see the island. We'll definitely be trying that again on our travels!