Lake Mashu Observatory

The 61-kilometer Mashu Kussharo Trail connects Lake Mashu's caldera viewpoint to Bihoro Pass on the western rim of Lake Kussharo, crossing volcanic landscapes shaped by eruptions over the past 300,000 years. The route passes Mt. Io, an active sulfur mountain with 1,500 fumaroles, and follows part of an old ore railway used during the late nineteenth-century sulfur mining boom. Ainu settlements once flourished along Lake Kussharo's shores, and the trail visits Kussharo Kotan village and several natural hot springs where Ainu people soaked bark for weaving thread. The walk typically takes three to four days.