Folder Earth
Earthen buildings, in their many forms around the world, can be thought of as clay-based concrete, as opposed to cement-based concrete. Many are, yes, mere mud huts, but many are magnificent architectural gems, and very effective as shelter.
And they are cheap, so that's what the poorest of the poor throughout history have had to use - thus the strong association of earthen building with squalor. But some of the most effective and lovely new structures anywhere are made with earth, signals of a worldwide renaissance of earthen architecture.
