6. Great Barrier Reef, Australia
This is the biggest reef barrier made up of over 2,900 separate reefs and around 900 islands spread over more than 1,400 miles and an area of around 133,000 sq miles. The offshore is located in the Coral Sea, near the coast of Queensland in Australia.
The Great Barrier Reef can be also seen from space and is the globe’s largest structure construed by living organisms. This reef is made up of, and built by tens of billions of small organisms, named coral polyps.