Mt. Kokureishin, often abbreviated to Mt. Koku, nicknamed The Snow Mountain, is the infamous black mountain in Hokkan where Nuriko fought Ashitare and died. Also the hiding place of Genbu's Shinzaho, guarded by the spirits of Hikitsu and Tomite until Miaka came to retrieve it. However, the terrain is all snow, and it is very cold.
This is also the place where Uruki was initially sentenced to die by the monsters, and the place where he meets Takiko.