While the Great Barrier Reef offers a bevy of watersports, island retreats, and offshore adventures, this is scuba-diving country above all else. And there’s not a diver alive who doesn’t fantasize about slipping below these celebrated South Pacific waters. But traveling to Queensland, Australia, for day-boat diving alone is like trekking to Everest base camp just to sit in a tent for a couple of hours. Book a liveaboard boat that heads to far-flung hot spots like Cod Hole and the Ribbon Reefs. These trips can run from four to seven days and include meals, accommodation, and up to five daily dives. The northern reef, with its shallow coral gardens, deep walls, and open-ocean bommies (reef pinnacles), hosts everything from Nemo-style anemones to swirling reef sharks. Come June or July, you can even swim face-to-face with dwarf minke whales.