Here's a picture of Mike, me, and my sister doing a combo quad-biking/sandboarding trip amongst the Namibian sand dunes in Swakopmund.
The three of us are riding quad bikes - ATVs that can roar up and down fragile dune ecosystems with frightening ease and speed. Granted, nothing much (that I can see) lives on the dunes we tore up, but I'm not sure if it was originally that way.
As for sandboarding, it involves going to the tallest, steepest dune around, and then sliding down on a piece of waxed plywood. (I have a picture of this, but I'm a small dot going down a hill, so it's not that interesting.)
Sandboarding feels surprisingly safe, although we're told that participants reach speeds of up to 80 km/hr. Anyway, it was a great rush and a great experience, despite the mouthful of sand I got when I foolishly opened my mouth to scream.