The Ngorongoro Volcano blew its top millions of years ago, leaving behind the world’s largest intact caldera. Inside the crater—covering more than 100 square miles—is an ecosystem that’s home to more than 25,000 animals. You’ll have a great chance of spotting lions, as there’s a higher density here than anywhere else on earth, along with leopards and cheetahs. Black rhinos are also a common sight, as are hippos, zebras, hyenas...the list goes on and on. Outside the crater, more than a million wildebeest sweep through during the Great Migration. See signs of our first known human ancestor, who walked these plains 1.9 million years, at nearby Olduvai Gorge.