Have made the trek up High Dune three times, all part of my road trips either going to or leaving Yellowstone from Atlanta. I always find a way to make it over to the dunes each summer, because it's like no other hike you can do anywhere else, unless you're in the Sahara.
Beautiful area, a bizarre part of Sahara at 2500 meters... I was lucky for the climb because it was the last day of sun before a storm. No wind and pretty mild with the sun, but still some snow in north slopes.
Just a great place, with the Crestones looming above. I liked climbing the steepest part of High Dune, it felt like I was going nowhere with every step but I eventually got there. Then run back down!!!
Did it early in the morning and had wonderful light for photography! But, it is harder than it looks, both because of the altitude (over 8,000 feet), and because the sand made hiking so difficult. Well worth the view from the top, however! You'll see parts of the park that can't be seen from anywhere along the main roads.