Which is the largest natural harbor in the world?

Sydney Harbour in Australia is the largest natural harbor in the world. It is also the location of many of the city's main attractions, including the Sydney Opera House, the Sydney Aquarium and the Sydney Harbour Bridge.

Over 11 miles long and covering an area 21 square miles in size, Sydney Harbour, in Sydney, Australia, is also called Port Jackson. The harbor is home to several islands, many of historical significance. It also houses a large variety of fish — totaling over 580 species. The harbor's large volume, approximately 500 gigalitres, is the base of the Sydharb, an official Australian unit of volume.