Mount Gassan is a stratovolcano in the ancient province of Dewa and the highest of the Three Mountains of Dewa. The Gassan Shrine stands at the mountain's summit, 1,984 metres above sea level. The hike from its trailhead to the summit usually requires about 4-5 hours and can be challenging. Visitors should be aware of the weather and not try to hi…Mount Gassan is a stratovolcano in the ancient province of Dewa and the highest of the Three Mountains of Dewa. The Gassan Shrine stands at the mountain's summit, 1,984 metres above sea level. The hike from its trailhead to the summit usually requires about 4-5 hours and can be challenging. Visitors should be aware of the weather and not try to hike it on days with wind or heavy rain. The trail is not paved and in some parts requires the use of hands to navigate certain parts of the trail.