On October 6, 1769—250 years ago today—Captain James Cook reached New Zealand on his first voyage to the Pacific. He would eventually map the entire New Zealand coastline, including the area here at Marlborough Sounds, a network of ancient sunken river valleys on New Zealand"s South Island. The main purpose of Cook"s voyage to the Pacific was to sail to Tahiti and observe the transit of Venus across the face of the sun. Only after completing this task did Cook unseal the rest of his orders and learn he was to search the South Pacific for signs of a fabled great southern continent, Terra Australis Incognito. European Renaissance geographers believed this hypothetical southern landmass must exist in order to counterbalance the Northern and Southern Hemispheres.