I hadn't heard of The Great Race of Mercy, so I looked it up. Apparently, it's a real event that took place in 1925. As it's set in the snow, it has a lot of potential for some interesting puzzles. As it's essentially a race against time to get the antitoxin delivered. I see it as a series of runs through the snow beset by the occasional mishap, such as getting lost, sled turning over or breaking, getting attacked by wolves, food getting lost and so on. Because your goal is to get from point A to point B, you'll have to be careful that you don't make it too linear.