Ubayu spa is a secret hot spring located in the deep valley in the north side of the Agatsuma mountain range and the altitude of the hot spring is 1300M high. The scene of the hot spring among the virgin forests is said to be the most beautiful in Yamagata and particularly the fresh verdure in spring and the colored leaves in autumn are wonderful. There was only one hot-spring hotel in Ubayu spa. In old days a mine operator who was the first generation of the hotel owner met a woman who had a long hair and bathed in hot water at an outdoor bath, when he went around in mountains for a vein and came over to this ground by chance. When he approached the woman fearfully, he was surprised to see her. The woman was a terrible mountain witch with a baby. When he try to run away, the mountain witch said that "Stop such unfortunate work, and become a spring operator of this hot spring" and she disappeared with the baby. Thereafter this hot spring was named Ubayu (mountain witch) spa and the tradition is handed down till now.
姥湯温泉は、吾妻連峰の北側、標高1300Mの奥深い谷間に位置し、南画世界を思わせる奇岩怪岩が聳え立つ絶壁に囲まれた秘湯です。
コメツガ・ブナ・ダケカンバなどの原生林に囲まれた温泉の景観は山形県第一といわれ、特に春の新緑・秋の紅葉は見事です。
姥湯温泉には一軒の温泉宿がありますが、鉱山師だった宿の初代が鉱脈を求めて山々を渡り歩いて偶々この地へやって来た時、露天風呂で湯浴みしている髪の長い女性に出会ったそうです。
こんな山奥で女が湯浴みとはと驚き、おそるおそる近づくと、なんと、その女は赤ん坊を抱いた恐ろしい形相の山姥(やまんば)であった。
思わず逃げ腰になると、山姥は「そんな因果な山師などやめて、この湯の湯守にならんかい」と云い残し、赤ん坊もろとも山姥の姿はどこかえ消えてしまいました。
それ以来、この湯を姥湯と名づけ、現在に至ると言い伝えられています。