The Great Barrier Reef, according to Sydney University historian Iain McCalman, is so vast the only people able to fully grasp its scale are astronauts.
The reef's network of hundreds of islands and individual reefs stretches more than two thousand kilometers from its northern tip in the Torres Straight almost halfway down the eastern coast of Australia.
Today when people think of the reef they think of a fragile natural wonder but in the past people have had a very different perspectives.
To Captain Cook it was a "nightmare labyrinth" which very nearly spelled doom for his voyage of exploration. To the aboriginal people islands on the reef were home, and the reef itself a vital source of food.
And in the fevered imaginations of europeans it was terra incognita - a place filled with fearsome cannibalistic tribes, shipwrecks and astounding tales of survival.
Iain McCalman talks to Kathryn Ryan about the reef's natural wonder. He will be doing a series of lectures around New Zealand later this year as a guest of the Royal Society