Kamuinupuri (カムイヌプリ), a mountain sitting on the southeastern shores of the Lake Mashu-ko (摩周湖) caldera, stands fewer than 1000 meters at its summit, but looking down its sheer faces, you might get the sense you’re on a higher mountain. Kamui nupuri is an Ainu name meaning ‘mountain of the gods’. The origins of the Japanese name mashu, however, are unclear.
The trailhead sits right next to the bustling Lake Mashu No. 1 Overlook (摩周 湖第一展望台, Mashuu-ko dai-ichi tenboudai). Lake Mashu-ko is famous for its fog and mists, but if the weather fine and clear you’ll be able to see the stark form of Kamuinupuri standing across the deep azure of the lake. The trail winds around the lake’s sheer green rim, so set your sights on the peak and you’ll be off.
The first half of the hike is very gently-sloping along a ridgeline, with the drop down to the lake on your left and the broad plains of East Hokkaido to your right. The trail here is lacking in many big trees, instead cutting through a veritable sea of Kuril sasa bamboo without much charm or change.
You'll reach the top of a bit of a hill at 683 m above sea level or so, and find neighboring Mt. Nishibetsu-dake (西別岳) right ahead of you, with the craggy Kamuinupuri much closer and off to the left. In the spaces between the sasa, you’ll also find a number of flowers blossoming in the wind—for example, woolly geranium, Kamchatka lily, and fan columbine. These flowers make this part of the hike very lovely in early summer.
Where the wide ridgeline meets the rim of the Kamuinupuri crater you’ll find the Mt. Nishibetsu-dake junction (西別岳分岐, Nishibetsu-dake bunki). Take the left path towards Kamuinupuri, and you’ll find the trail start to climb in earnest.
The area around the summit is dangerously steep, so the trail winds around the east side of the summit before doubling back to the summit of Kamuinupuri. Looking northward, the drop to the lake below is particularly precipitous; looking past the cliffs to the huge crater of Mashu-ko should illustrate sufficiently the tremendous power of the volcanism at work here.
Here's a short story from the annals of history. In 1857, in the later days of the Edo Period, Hokkaido explorer Matsuura Takeshiro (松浦武四郎), along with an Ainu guide, started out from what is now the lookout point at Ura-Mashu Overlook (裏摩周展望台, Ura-mashuu tenboudai) and walked counterclockwise around the lake, climbing Kamuinupuri from the south. In his Kusuri Nisshi (久摺日誌) journals from 1861, he told of a brutally dangerous approach up the face of the mountain, and a summit that found him and his guide bloodied, their clothing torn and ragged. Linger at the summit a little while, detach from the hustle and bustle of city life, and you might just feel the summit of so many years ago floating vaguely before you.
The way back follows the route you took up. If you can suss out leaving a car at either end, and if your legs feel up to the trip, the trek from Nishibetsu-dake junction across to Mt. Nishibetsu-dake is a great trek.
In June and July, the flowers will be out en force: it’s likely you’ll see fan columbine, Kamchatka lily, woolly geranium, and keyflower. Near the summit you might see some Japanese veronica. The leaves change color in late September and continue changing into October.