Opened in 1932 together with the Kamimiyori ~ Yunokami section of the Aizu Line; this is the only one of the original Aizu Line tunnels still in use in its entirety.
The tunnel is between No. 3 Ōkawa Bridge and the Onogawa Bridge just to the north of Yunokami Station. Given they originate from the same time, I think it's safe to assume that the construction method was the same as for the Onumazaki tunnels, with the original tunnel wall being made entirely of concrete bricks, with a lining of poured concrete up until about halfway up the side walls. Later, the poured concrete layer on the lower half of the walls was given an extra layer, and a layer of wooden boards was applied to the arch of the ceiling where the brick was exposed; this was fastened in place by iron ribs that ran all the way around the arch from floor to floor.
トンネルは上三寄駅から湯野上駅までの路線部分と一緒に開かれた。会津線の元のトンネルたちからまだ使用されている唯一のトンネルである。
トンネルは湯野上駅のすぐ北で第三大川橋梁と小野川橋梁間である。他のトンネルのようにトンネルの元の壁はコンクリートレンガで作られた、壁の下半分にて注いたコンクリートの裏地があった。後ほど、コンクリートの裏地で追加の地層付け加えられた、と丸出しレンガは木の板で覆われていた。木の板は鉄の肋骨で開催された。