This is a fairly simple answer, they made snow goggles. They were in fact the first known people in the world to do so. They're basically a pair of goggles made from driftwood, bone or antler with a narrow horizontal slit. The oldest examples I'm aware of are from some time around the 11th century but that doesn't mean the knowledge of how to make them isn't far older. Today they've largely been replaced with modern sunglasses but the word for these goggles is the same as that for sunglasses.