Located at the foot of Kotani Castle, this hidden hot spring is a historic hot spring where Nagamasa Asai, a warlord of the Warring States period, is said to have visited for a hot-spring cure. The hot spring is said to have been used by warlords during the Warring States period to heal their wounds, and is highly regarded for its beneficial effects. It is known as the first "free-flowing" hot spring in the prefecture. In the Kohoku region, the Kannon (Goddess of Mercy), which has been protected by the pure hearts of the common people since the ancient Asuka period, still quietly exists today. It is said that the Kannon-sama has watched over the conflicts between warlords during the Warring States Period and the fall of Kotani Castle with a quiet gaze. The hot springs of Sugadani have been healing the hearts of people together with this Kannon-sama since ancient times. Warlords of the Warring States period and their wives, who were worried about their safety, must have sought a moment's peace of mind at Sugadani no Yu. It is a place where all visitors can relax in body and soul.