Mount Nantai, also called Futarasan, is a stratovolcano in the Nikko National Park in the main island of Japan. It stands at 2,486 m high. The mountain is popular with hikers, and the trail to the summit starts through a gate at Futarasan Shrine's Chugushi (中宮祠, middle shrine). The gate is open between 5 May and 25 October.
Mount Nantai is selected as one of the 100 famous mountains in Japan.
In September 2008, the Japan Meteorological Agency was asked to reclassify Mount Nantai as "active" based upon work by Yasuo Ishizaki and colleagues of Toyama University showing evidence of an eruption approximately 7000 years ago.
Archeologists affirm that during the Yayoi period the most common go-shintai (御神体, a yorishiro housing a kami) in the earliest Shinto shrines was a nearby mountain peak supplying with its streams water, and therefore life, to the plains below, where people lived.
Mount Nantai constitutes Futarasan Shrine's go-shintai, and the shrine is an important example of this ancient type of mountain cult. Significantly, the name Nantai itself means "man's body". The mountain not only provides water to the rice paddies below, but has the shape of the phallic stone rods found in pre-agricultural Joumon sites.