Kailua Bay is right at the main pier in town. You can drive right up to it, there will be a guard at the pier gate who you'll need to ask if you can drop off gear. Two-Dollar honor-box parking is right across the street or you can park at the hotel pay lot or at the free lot a 5 minute walk away. To the left of the pier (looking outward) is a nice shallow reef with a super easy entry. Follow the swim buoys out 'til you hit deep enough water to drop down and then dive. This winter there was a huge school of fish hanging out in 15' of water for several months...one could have their own "National Geographic Moment" sitting in the middle of tens of thousands of 10' schooling silver fish. This dive maxes out at about 20-25 feet. Don't bother if a cruise ship is in, the tenders kick up lots of sand. On the right side of the pier is the small boat ramp. Walk out the beach on this side and dive along the bottom - to avoid boat traffic. Once you reach the end of the pier head a bit to the right and there is a nice reef where you can hit about 60 feet if you'd like. In either case, take a dive flag and avoid boat traffic. The right side of the pier can be a great night dive, watch out for dive boats coming back from the manta dive about 1.5-2 hours after dark.