Mount Nantai(男体山,Nantai-san?) literally "man's body mountain", also called Futara-san (二荒山?) is a stratovolcano in the Nikkō National Park in central Honshū, the main island of Japan. It stands at 2,486 m high. A prominent landmark, it can be seen on clear days from as far as the Pacific coast, 100 km away.
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 (男体?) 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 Jōmon sites.