Great Barrier Reef, Australia

The Great Barrier Reef is the world's biggest coral reef system, with over 2,900 distinct reefs and 900 islands spanning over 2,300 kilometers (1,400 miles) over a 344,400-square-kilometer region (133,000 sq mi). The reef is located in the Coral Sea, off the coast of Queensland, Australia, and is separated from the coast by a channel that is up to 100 miles wide and over 200 feet deep in some spots. The Great Barrier Reef is the world's largest single structure built by living beings and can be viewed from space. Hundreds of billions of microscopic organisms known as coral polyps make up this reef structure. It was designated as a World Heritage Site in 1981 and supports a vast variety of life.

It was added to the list of Australian World Heritage Sites in 2007. In 2006, the Queensland National Trust designated it as a Queensland state icon.

The Great Barrier Reef Marine Park protects a substantial portion of the reef, reducing the impact of human activities like fishing and tourism. Runoff, climate change with mass coral bleaching, dumping of dredging muck, and cyclic population outbreaks of the crown-of-thorns starfish are some other environmental stressors on the reef and its ecosystem.

The reef is a major tourist destination, particularly in the Whitsunday Islands and Cairns areas. Tourism is a significant source of revenue for the region, contributing approximately AUD$3 billion annually. In November 2014, Google launched Google Underwater Street View in 3D of the Great Barrier Reef.

Location: Off the east coast of the Queensland mainland, Australia