The Great Barrier Reef is, of course, one of Australia's biggest attractions. This is a "mecca" for scuba divers and the marine environment attracts hundreds of thousands of visitors every year. Actually it is not a single unbroken coral reef, but a series of "small" barriers that extend for nearly 1000 km off the coast of Queensland. Given its size, there are many points from which to access it. Many people choose to visit the barrier near Cairns, since they're closer to large population centers. But it is also possible to visit observation decks of the barrier near the Whitsundays, like Reefworld at Hardy Reef.