I went to Heron Island many years ago, before they updated the one resort, and it was an amazing place! Take the helicopter over to see the views of the reef and do all the diving and snorkeling you can while there. We are only snorkelers but thoroughly enjoyed it. It's actually an atoll and you can walk around it in about 20min. Think we stayed 3 or 4nights which was plenty and I've heard since then the resort is much nicer and updated now. Don't miss the Bay Bugs for dinner either!