A lone black rhino is dwarfed by its surroundings in the world famous Ngorongoro Crater. The crater's 102-square-mile floor is spectacular for wildlife. This feature 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 the walls of a volcano standing about 15,000 feet high. Ngorongoro was declared a World Heritage Site in 1978.