Arguably the number one reason to visit Namibia is to come and see Deadvlei. It's a white clay pan in the midst of some of the largest sand dunes in the world. Formerly an oasis, the Tsauchab river which supplied water changed course hundreds of years ago leaving the acacia trees to die. The trees, which are estimated to be 900 years old, are not petrified but have been scorched black by the sun and the wood has not decomposed as its extremely dry here.
If you spend the night at Sossus Dune Lodge, which is run by the Namibian government, you get access to Deadvlei & Sossusvlei about an hour earlier than other tourists, which is highly worth it. On the morning I visited, there was only one other tourist there before sunrise leaving both of us free to roam and photograph the area without interruption.