High Dune - Great Sand Dunes NP, CO 

Hiked this just a few days after doing a R2R of the GC. Would say that the uphill on the dune was much worse than the climb out of the GC for sure. You do have to stay on the ridges for a better climb, but depending on how things go, you get into sections where the back sliding is quite bad and to make reasonable progress, you have to run up before you slide back and that is taxing. Incredibly unique sights and view and it's like that just pop up out of nowhere.