In numerous wuxia stories, there is the idea of "Five Elements Octagon"...basically traps set by the proper placing of the five elements (i.e. earth, metal, fire, water, wood). The Peach Blossom Island folks from Jin Yong's universe use it most prominently.
But what is it, really? It seems more feng-shui, sorcery, and pseudoscience than martial arts. What place does it really have in kung fu? Why is it a recurrent motif in wuxia fiction?