How to Build an IglooAn illustrated guide to constructing everything from igloos and quinzees to spruce traps and snow trenches. How are the ice blocks of igloos so perfectly formed and fitted, 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 to make a slab shelter with as a snowman? What is a slab shelter, anyway? For that matter, what are drift caves, spruce traps,