The world famous Ngorongoro Crater. Its 102-square-mile crater floor is the haunt of a wonderful wildlife spectacle. The crater is in fact a 'caldera' _ the largest unbroken, unflooded caldera in the world _ which was formed two and a half million years ago when a huge explosion destroyed a volcano standing about 15,000 feet high. Ngorongoro Crater was declared a World Heritage Site in 1978.