The star attraction of Namibia’s Namib-Naukluft National Park is this claypan surrounded by soaring, ever-changing red-orange dunes that stop the flow of the Tsauchab River. In the native language, Sossusvlei means “dead-end marsh.” The dunes that circumnavigate the pale flat, dotted with leafless vegetation, are some of the loftiest and oldest in the world. Many are well over 650 feet tall and thought to be 5 million years old. While the dunes vary in color, the ones displaying the brightest shades of red—indicating a high concentration of iron—are the oldest.