The Great Barrier Reef is the largest living thing on Earth and is one of the 7 Natural Wonders of the World. The amazing coral reef system stretches 2,300 km and supports a diverse range of life. I would suggest booking a day cruise tour which takes you out to the reef, provides lunch and snacks and offers snorkelling and water sports. Cairns and Port Douglas are the best cities to stay at to access the Great Barrier Reef. #onceinalifetime