Set in the eastern branch of the Great Rift Valley, Olorgesailie is one of Kenya's best-known archaeological sites. Discovered in 1919 by geologist J. W. Gregory, the area was excavated by Louis and Mary Leakey in the 1940s. They discovered tools thought to have been made by residents of the region more than a half million years ago. A small museum shows some of the axes and other tools found nearby. The journey here is unforgettable. As you drive south on Magadi Road, you'll find that past the town of Kiserian the route climbs over the southern end of the Ngong Hills, affording fine views of the entire valley. Volcanic hills rise out of the plains as the road drops into dry country where the Masai people graze their herds.