6. The Great Barrier Reef – Australia
Located in the Coral Sea, the Great Barrier Reef in Australia is the largest coral reef system of the world. Included in the system are more than 3,000 reefs and 900 islands that stretch over an area of 344,400 square km approximately. The amazing thing about the reef is that it can be seen even from outer space. It is the biggest natural structure that is made of living organisms. It has been declared as a World Heritage Site since 1981.
