Wool is a post-apocalyptic novel by Hugh Howey. In it, the world is all fucked up and people (all of the remaining people, presumably) live in giant underground silos. Nobody knows what happened to the earth, or why everyone lives underground, and indeed everyone in the silo where all the action happens thinks that their silo is the only one in existence. This proves to be false, of course, along with a bunch of other stuff they believe. Wool is pretty good, and was a gripping read for most of its length, but was ultimately disappointing in several key ways.