Its Olduvai Gorge region is known as the "cradle of humanity," the site of the earliest known human habitation. The arid Sahara is Earth's largest desert. Mt. Kilimanjaro, despite its proximity to the equator, is tall enough to sport glaciers, though they are rapidly melting due to climate change (scientists hope to combine the new elevation data with other satellite imagery of the area to better monitor and understand the environmental changes taking place there). The Great Rift Valley is one of the world's longest earthquake faults. Lake Victoria is the second largest freshwater lake in the world behind the U.S. Lake Superior. The Congo Basin is home to the second largest concentration of rainforests on Earth behind South America's Amazon. And, of course, there are the great savannas, such as the Serengeti, which teem with some of Earth's most exotic wildlife, including plenty of those elephants.