Mountains have been worshiped in Japan since ancient times. Similar to Mt. Fuji, Mt. Ontake has been a site of worship ascents since the Edo era. We previously examined the style of mountain huts on Mt. Fuji during the Edo era, and in the present study, we have expanded our scope to Mt. Ontake. We conducted field surveys on the Kurosawa and Otaki trails on Mt. Ontake and found a common architectural characteristic, the so-called “central path style” floor plan (or “Nakadori style”), in which the trail passes through the mountain huts. A previous study reported that this floor plan is similar to that of somagoya (loggers’ huts) in this area. Therefore, we examined historical materials and investigated the establishment and transformation of this “central path style” floor plan and the relationship between mountain huts for worship ascents and forestry.

 Many mountain maps drawn in the Edo or Meiji era have legends showing mountain huts on as opposed to beside trails, suggesting that the “central path style” floor plan might date back to the late Edo era. Mountain huts were first donated as guardian huts around holy places, places for religious training, and shelters against the harsh mountain environment. They were then expanded to serve as teahouses or lodgings. In addition, many of the mountain huts on the Otaki trail had the “central path style” floor plan since the Meiji era. Since the Edo era, residents of Kurosawa and especially Otaki village in Kiso valley earned their living by felling trees. The loggers’ huts in Kiso had a “central path style” floor plan and was called “Nakagoya”. Both trails had a mountain hut for worship ascents called “Nakagoya.” It seems that the “central path style” floor plan we discovered on field surveys was inherited from somagoya, based on the livelihood of the residents.

 On the other hand, we found another, lost architectural characteristic from old documents called the “double hut style” floor plan (or “Ryogoya style”). At Tanohara on the Otaki trail, two huts were found opposite each other on the trail from the Edo to the Meiji era. However, by the Taisho era, the space between the huts was covered and changed into an interior, i.e., the “central path style” floor plan. We found a similar religious building with a “double hut style” floor plan on the Yoshida trail on Mt. Fuji. Since the Edo era, both the Tanohara Ryogoya on Mt. Ontake and the haiden (front shrine) of Fuji Omuro Sengen Jinja on Mt. Fuji were used as komorido, where ascenders, especially women, would chant, practice abstinence, and sleep. Thus, it seems that the “double hut style” floor plan was universally established for mountain worship.

 Mt. Ontake is an object of worship for believers and provides a living for local villagers. The mountain huts that have supported worship ascents since the Edo era have architectural characteristics related to mountain worship and livelihoods. Both the “Ryogoya” and “Nakadori” styles have a strong connection with huts and trails, and this is a special characteristic of the mountain huts on Mt. Ontake.

 After the volcanic eruption of Mt. Ontake in 2014, some mountain huts on Kurosawa and Otaki trails were closed, demolished or reconstructed. We hope the results of our research help preserve traditions of the mountain huts on Mt. Ontake.