Needle-Grinding Temple was built according to a Taoist legend that Prince Zhenwu became disheartened after several years of self-refining when he met the God of the Purple Primordial Sovereign who disguised himself as an old woman and the old woman was grinding an iron rod on purpose. Zhenwu asked the old woman what she was grinding the iron rod for and he got a reply that “perseverance spells suc...