Book excerpt: How are the ice blocks of igloos so perfectly formed and fitted, and able, it’s been said, to withstand the weight of a polar bear? How can you determine if the fresh snow that’s fallen outside your front door is as good for making a slab shelter as a snowman? What is a slab shelter, anyway? For that matter, what are drift caves, spruce traps, snow block walls, and bivy bag shelters, and how would you go about building them, whether for winter fun or protection from the weather? In this instructive, whimsical, illustrated manual, Norbert E. Yankielun, a seasoned cold-regions explorer and researcher, takes readers step-by-step through the process of constructing and inhabiting a range of useful snow structures—from the most basic to the more complex. Whether you’re a veteran backcountry skier or a backyard builder, this is one book you won’t want to be without.