Time Required: 1 h 5 min. Distance: 2.8 km
Mt. Iwosan gets its Ainu name, Atosanupuri from the words atosa ("naked") and nupuri ("mountain"). Even now, more than 1,500 fumaroles of various sizes vigorously vent steam on Mt. Iwosan. On this course, you will visit the mountain via the lush Tsutsujigahara Nature Trail. As you walk the trail, you can see Mt. Iwosan on your right, the Kussharo Caldera to your left, and if the weather is good, Mt. Sharidake will make an appearance in the distance. Along the way are Haimatsu Deck and Isotsutsuji Terrace where you can enjoy the flowers of Ledum Palustre var. diversipilosum and the dwarf stone pines from June to July.
Kawayu Eco-Museum Center provides information about the natural environment in the Mashu and Kawayu areas of Akan-Mashu National Park. There are helpful staff on duty, a lounge space where you can relax by the fire, and a café on the second floor, allowing you to take your time and look around. You can also visit the free footbath along the hot spring river — about a one-minute walk from the Eco-Museum Center — where you can soak your legs in Kawayu Onsen’s acidic hydrogen sulfide spring and acidic sulfur spring.
As you approach Mt. Iwosan, the nature trail passes through a dwarf stone pine zone, a Ledum Palustre var. diversipilosum zone, a broadleaf forest zone, and a conifer zone. Due to the fumarolic and hydrogen sulfide gases emitted by Mt. Iwosan and the strongly acidic soil, the mountain presents an unusual ecosystem. The stark changes in vegetation are easily noticeable, and although the elevation is relatively low at 150 meters, you can find alpine fauna such as the dwarf stone pines and Ledum Palustre var. diversipilosum.
As the name Iwosan ("sulfur mountain") suggests, the distinct smell of sulfur hangs in the air at Mt. Iwosan (512 meters). Sulfur was once mined on this mountain and it has more than 1,500 fumaroles of various sizes that actively spew out white volcanic gases. At the Mt. Iwosan Rest House in the foothills, make sure you try one of Mt. Iwosan’s famous onsen tamago (hot spring eggs) that are cooked with the water from Kawayu Onsen. In fact, it is customary to first eat one of these eggs whenever visiting this area. The iwodama, snacks made to look like lumps of sulfur, are very popular, too.