Located at a height of 1,400 meters in Nikko National Park, Senjogahara is one of the largest highland marshes on Honshu. Originally a lake formed by an eruption of Mt. Nantai, Senjogahara evolved into 400 hectares of marsh over time. More than 350 species of native plants and wild birds inhabit the area, and 175 hectares of the marshland is part of Okunikko Shitsugen, a registered Ramsar site. A nature trail offers easy hiking through the marsh. A particularly beautiful time to visit is the middle of June to the beginning of August when cottonsedge and meadowsweet are in full bloom, as well as the end of September to the beginning of October when the marsh grasses turn red.