Hitoana (Hitoana Fuji-ko Iseki)
Unlike the various tainai tunnels, the Hitoana cave was widely known long before the first Fuji-ko confraternity was founded. As early as the thirteenth century, records called it the home of Sengen Daibosatsu, deity of the mountain, and a commonly circulated illustrated story told of a samurai who traveled through it to the underworld.
The Hitoana is a hushed, mysterious cavern, high enough to stand in. Its floor is permanently covered in water. In the early seventeenth century, it was used as a site for ritual practice by the ascetic Hasegawa Kakugyo (1541?–1646), who spent 1,000 days meditating on a wooden block inside the cavern, according to the traditional account. From the mid-eighteenth century, as the Fuji-ko network spread, growing numbers of pilgrims visited the Hitoana as a kind of sacred site for showing respect to Kakugyo, spiritual founder of their faith. Over 200 stone monuments left by these pilgrims still stand by the entrance.
Today, the Hitoana is administered by the Fujinomiya City Board of Education. It can be visited by advance appointment, except in winter.