The Ngorongoro Crater is the remnant of a large volcano that “blew its top” and thank the cosmos it did because today it is home to nearly every animal native to East Africa including the Big 5, not only that but they are less shy which means you can get closer to them than in many other places and with the floor 260km² and an estimated 25,000 large animals inside you are guaranteed to see plenty of wildlife in addition to the unique cradle of life that is the crater itself.
Google Earth Placemark - http://bbs.keyhole.com/ubb/download.php?Number=61364
Wikipedia article for Ngorongoro Crater - http://en.wikipedia.org/wiki/Ngorongoro_Crater
UNESCO page for Ngorongoro Crater - http://whc.unesco.org/en/list/39
