What are your cool sparsely populated lands?

In my case it would a vast desert that dominates the supercontinent. On one side of the land mass a large mountain range separates a lush verdant costal region for a barren desert. You don’t have to go far from the mountains or the the oasis to find seemingly endless sand seas. Human life clings to one great railway that stretches from the mountain all the way to where the desert gives way to coast on the other side. It's as long as the Great Siberian Railroad.