A UNESCO World Heritage Site, The Ngorongoro Conservation Area is located in Ngorongoro district, 180km west of Arusha city in Arusha region, within the Crater Highlands geological area of northern Tanzania. The name of the crater has an onomatopoeic origin; it was named by the Maasai pastoralists after the sound produced by the cowbell (ngoro ngoro). Ngorongoro Crater is the world’s largest inactive, intact and unfilled volcanic caldera. The crater, which formed when a large volcano exploded and collapsed on itself two to three million years ago, is 610 metres (2,000 feet) deep and its floor covers 260 square kilometres (100 square miles). Estimates of the height of the original volcano range from 4,500 to 5,800 metres (14,800 to 19,000 feet) high. The crater floor is 1,800 metres (5,900 feet) above sea level. The crater was voted by Seven Natural Wonders as one of the Seven Natural Wonders of Africa in Arusha, Tanzania, in February 2013