Not only did Jiufen's hilly terrain create many parallel roads at various altitudes, it also created the need for many tiny paths connecting these roads. This is the unique phenomenon of the "penetrant alley". A penetrant alley refers to "a narrow pathway found between houses or arcades". Based on this characteristic, we can categorize it in three groups: the first group consists of pathways sandwiched between two residential homes; the second group are the paths underneath residential houses, as if one is walking through an arcade or a mining tunnel; and the last group consists of steps between houses that connect two major roads.These penetrant alleys were a direct response to the large amount of immigrants during the heyday of the gold rush and the densely built housing communities such a sudden jump in population created.
