Mount Nanatsuishi, Mountain summit in Okutama and Tabayama, Japan

Mount Nanatsuishi is a 1,757.30 m peak on the border of Tokyo and Yamanashi Prefecture, listed among the Kai Hundred Mountains. Near the summit stand the Nanatsuishi Hut, Nanatsuishi Shrine and a water source; a summit marker was placed in 2016 to mark the establishment of Mountain Day. The ridge route continues to Mount Kumotori in about 1 hour 35 minutes.

The summit area holds the Nanatsuishi Shrine and the Nanatsuishi Hut, a mountain lodge run by Tabayama village with overnight stays and tent pitches. In 2016, to mark the creation of Mountain Day, a summit marker stone was placed on the 1,757.3 m top. The mountain is listed among the Kai Hundred Mountains.

The name Nanatsuishi, "seven stones", refers to the rocks that give the summit its name. Near the top stand the Nanatsuishi Hut, a mountain lodge run by Tabayama village with overnight stays and tent pitches, and the small Nanatsuishi Shrine, where walkers on the Okutama ridge route stop. The hut is about 30 minutes below the summit.

The hike to the summit takes around three and a half hours from Kamosawa bus stop and requires moderate fitness. The mountain hut located on the route offers a place to stay for visitors planning a longer mountain experience.

The summit marker was placed in 2016 to mark the creation of Mountain Day, a Japanese public holiday. Near the top stand the Nanatsuishi hut, a shrine and a water source; the hut, run by Tabayama village, is 30 minutes below the summit and offers overnight stays, camping and a composting toilet.