One of my reasons for going to Namibia has always been to see some of the most spectacular sand dunes in the world. Many of them are over 200m tall, with the tallest one being about 380m tall (it's sand...so it shifts and changes). Even though I'm not sure how tall this one is, it's tall enough to make those trees at the bottom look quite tiny in comparison.
The color of the dune is a bit more orange/reddish due to the iron in the sand, and the iron oxidizing. Much more attractive dunes than those plain ones in the Gobi (no offense, Mongolia).
Sand dune in Namib-Naukluft National Park, a UNESCO World Heritage Site