A short sail out from Waikiki brings you to reef ground where green sea turtles come to feed and be cleaned by reef fish. They are large, unhurried and entirely indifferent to swimmers, which makes for one of the calmest wildlife encounters in Hawaii.
The boat anchors above the reef, crew fit your mask and fins and run through the briefing, and then you are in warm, clear water over coral. Flotation belts and noodles are available for anyone unsure of themselves, and crew stay in the water to keep an eye on things and point out what you might otherwise swim past.
Turtles are protected by law here, so you watch from a respectful distance rather than reaching out — which is no loss at all, since they frequently surface a few metres away to breathe before sinking back down to the coral.