The Great Barrier Reef is located in the Coral Sea off Queensland's East Coast. It spans a massive 2,300 kilometres and features 2,900 individual reefs and 600 continental islands. (It’s so big that it can be seen from space.)
All of these destinations have daily flight connections to major Australian cities. If travelling from overseas, you’ll most likely have to transit through Brisbane. Public transport may also be available depending on which state you’re coming from.