The Great Barrier Reef is the world's largest coral reef ecosystem. It stretches more than 2,000 kilometers along the eastern coast of Australia. The Reef is so big, it can be seen from outer space! The Great Barrier Reef is made up of more than 3,000 coral reefs, which account for its great variety of sea and animal life. More than 600 beautiful islands are scattered along the Reef. Visitors can explore rain forests or go snorkeling. (JEFF HUNTER—GETTY IMAGES)