This highly visited African attraction is the world's largest inactive, unbroken and unfilled volcanic caldera. This explosion created a caldera approximately two and a half million years ago.When it was a volcano it’s thought to have been a similar size to Mount Kilimanjaro, one of the world’s highest mountains. Estimates of the volcano’s original height vary between 4,500 to 5,800 metres. The crater itself is about 610 metres deep and 260 kilometres squared.