The Kalahari Bushmen, or San people, hollow out the branches of the kokerboom tree and use them to create quivers to carry their arrows in. Thus, these trees, which are actually aloe dichotoma, are known as quiver trees. To me, they look like they'd be right at home on some alien planet.
The quiver trees are somewhat rare, and are actually endangered. They also don't tend to grow in forests, which is what makes the quiver tree forest outside of Keetmanshoop so unique. You can really see a bunch of these old trees which is great. As I would drive throughout the Namibian countryside, I would once in a while see a lone quiver tree.
The way my itinerary worked out, I was visiting the forest in the morning, but really it's much better to visit around sunset, and I've seen some stunning photos of the trees lit up by the stars at night. If you visit, try and view it at sunset at least!
Quiver Trees in the morning.