Eternal land, tokoyo no kuni. An other-world, either across the sea or a realm of its own beneath the water, equated with the dragon's palace, ryugu, inhabited by beneficent and demanding spirits including spirits of the dead and particularly transforming snakes. Inland, Tokoyo came to be located in the mountains rather than the sea, forming the other-world of mountains which, combined with Buddhist cosmology, was the basis of mountain religion (see Shugendo, Yama-no-kami).
A Popular Dictionary of Shinto. Brian Bocking.