The Great Barrier Reef is the biggest reef in the world, stretching at over 1300 miles long and 40 miles wide. The coordinate points of the reef are 18.2861° S, 147.7000° E. The reef isn't one big island of coral, but rather many islands of coral. It has over 2000 individual reefs and is built on a foundation of coral that is about 18,000 years old.