While on my self-drive road trip through Namibia, I made a stopover in Swakopmund while driving from Sossusvlei to Damaraland. Giving the distances and time, it's pretty much required. I spent an extra day in Swakop to see the area, although I wish I had 2 days. The area is a popular spot for a number of fun activities - great surfing, quadbiking, duneboarding, skydiving - it has it all.
I did a day trip to Walvis Bay and Sandwich Harbor. While the dunes there aren't as big as in Sossusvlei, there's 4x4 tours that drive through them which is pretty cool! In Sossusvlei, you more so drive through a road between the big dunes, so this is way more extreme and exciting in comparison.
Land Rovers make their way through sand dunes.