Mt. Nishibetsu-dake (西別岳, Nishibetsu-dake) is a high, broad-topped mountain massif just to the southeast of Lake Mashu (摩周湖, Mashuu-ko) and sits at the headwaters of the Nishibetsu River (西別川, Nishibetsu-gawa), which flows windingly eastward and empties into Nemuro Bay at the town of Honbetsukai (本別海). It’s said that the Nishibetsu River is fed by Lake Mashu’s aquifer system; apparently, its waters are also famously salmon-flavoured. The word nishibetsu itself is said to come from Ainu nu-ushi-pet, meaning 'river with fish aplenty.' (Fisherman take note.)
Nishibetsu is probably the best place to view the sharp form of Kamuinupuri (カムイヌプリ, also called Mt. Mashu-dake, 摩周岳 Mashuu-dake); it's especially picturesque against the wild grasslands of the mountain’s plateau. That being said, the ease of access and family-friendly nature of the trek draw visitors en masse, which is doing no favours for the low alpine environement. Please stick to the trails and be very carefuly not to tread on any of the small flowers lining the path.
There are two trails to the summit. The first starts at Nishibetsu Hut (西別小屋, Nishibetsu-koya) in Shibecha Town (標茶町, Shibecha-cho); the other starts at the Lake Mashu No. 1 Overlook (摩周湖第一展望台), far off on the other side of the massif. As a significant portion of the walk from the Mashu Overlook is covered in the Kamuinupuri guide, this hike will cover the climb up from the hut.
Take Prefectural Route 885 (道道885号線, Doudou 885 gousen) and turn off at the wooden sign for the trailhead, following a narrow track to the hut.
You’ll start the hike in a forest of Japanese larch, but shortly emerge from the forest and start the climb up to the ridge above you. The mountain is mostly covered only with sasa bamboo (Sasa veitchii, ササ), so once you've passed through the lowland forests, you’ll have wide open lines of sight in every direction. The long hill up to the top of the flat massif is locally called “Endurance Hill” (がまん坂, gaman-zaka), so fight your way to the top and you'll be rewarded with the whole of Eastern Hokkaido’s broad farmland spread out before you.
At the top of the hill you’ll follow the ridge through a stand of young Erman’s birch and climb the short rise to Risuke-yama Junction (リスケ山分岐, Risuke-yama bunki), named after the minor peak you'll skirt along here. Around Mt. Risuke-yama you may spot a number of small flowery meadows, featuring Swertia tetrapetala, Metanarthecium luteoviride, and Kamchatka rhododendron. If they're looking a little sparse, blame the hipsters that pick the flowers and wear them in their hair for the IG cred.
(All kidding aside, the flowers up here don't grow back next year if you pick them. Take only pictures, folks.)
From Risuke-yama onwards it’s a gentle stroll along the ridgeline. The low, broad ridgline between Risuke and Nishibetsu is called Gokuraku-daira (極楽平), and it's probably the most lovely spot for a touch of Kamuinupuri-viewing. The little purple-red Pedicularis japonica grow in bunches near the summit of Nishibetsu-dake, making an early-summer trip up the mountain a delightful one.
You can head back down the mountain the way you came; but if you continue along the trail past the summit, you’ll wind up at the Kamuinupuri junction, where you can climb to the summit of Kamuinupuri and/or head to the Lake Mashu No. 1 Overlook. If you can manage it, the full traverse to the Overlook is worth the trek.
Because Nishibetsu-dake is not particularly tall nor the trail particularly difficult, the hiking season lasts quite long. The flowers are at their best from late June and into July. Along the ridgeline you’ll probably see beachhead iris, Kamchatka rhododendron, chickweed-wintergreen, grass-of-Parnassus, and Pedicularis japonica. The leaves start changing color in mid-September.