Shadow is a wonderful concept of vision -- if there's no shadow, we won't be able to figure form nor texture. Shadow gives us relief from too much brightness, or too much heat. We still treat shadow as being the evil itself, but you can perfectly survive in a sunless cave while you'll dry up in no time staying in open sunshine in a hot desert of your choice.
Limit #25 Fearing The Dark
Walls make for great sun-blockers as they throw perfect shadows. Sitting in the shadow of a wall enjoying a soft breeze is pretty much the best you can do on a hot summer's noon. And while on it study the nice calculations the carpenter left when building this wall lit be a lone lamp.