The lunar world where the Moonlight family lived was five times larger than the Three Extremes Sect. There were forests, rivers, areas with active volcanoes, regions covered by a sea of rays, and much more. Despite everyone in this family having a talent for using mental powers, they weren't limited to just that and specialized in two or more areas.
According to Ruri, in other families there should be even more diverse places dedicated to teaching Yin and Yang, laws of space and time, and other specialties. For example, the Yangta had a cemetery where all the ancestors left their legacies and knowledge for the new generations.
