Whether young or old, triathlete or couch potato, everyone appreciates the island's most easy-to-access (and admittedly busy) snorkeling spot. Protected by an ancient breakwater (which, according to legend, was built by the menehune, or 'little people'), the bay is pleasantly calm and shallow. You'll spot tropical fish and honu (green sea turtles) without even trying. The lifeguard-staffed park has outdoor showers, restrooms, drinking water, snorkel and locker rentals and picnic tables. Water can sometimes get cloudy later in the day.
Kahaluʻu can be too popular for its own good, with snorkelers literally bumping into one another. The salt-and-pepper beach (composed of lava and coral sand) is often a mass of humanity, which you may find sociable or nauseating, depending. Come early; the parking lot often fills by 10am. Treading lightly is also important: follow coral-reef etiquette. By law you must stay at least 50yd from all sea turtles in the water (20ft on land).
When the surf's up (and it can rage here), expert surfers challenge the offshore waves and avoid strong rip currents on the bay's north side near the church. When conditions are mellow, beginners can learn to surf or stand up paddle surf.