Oku Daisen is a highland plateau on the south side of Mt. Daisen, surrounded by beech forests. One section of the plateau, known as Kagamiganaru, supports a rare example of a high-elevation wetland. This marsh, located at 920 m elevation, is fed by water flowing down from Mt. Karasugasen (1448 m), Mt. Zoyama (1085 m), and Mt. Giboshi (1110 m). Alongside the marsh are grasslands that are home to a variety of wildflowers, including fields of Japanese silver grass (Miscanthus sinensis), that in autumn turns the area into a shimmering silver sea. The water of Oku Daisen is naturally filtered and purified as it seeps through the beech forests, and it serves as the region’s water supply. Since 1974, restoration projects have been carried out to revitalize the wetlands.