The Great Barrier Reef off the coast of Queensland is the world's largest reef system composed of over 2,900 individual reefs and 900 islands stretching for over 2,600 kilometres. The Sydney Opera House, built by Danish architect Jorn Otzon, is a performing arts centre in Sydney and is considered one of the great buildings of the 20th century. Aboriginal people arrived in Australia over 50,000 years ago and still use instruments like the didgeridoo, a wind instrument developed in northern Australia at least 1,500 years ago.