Mt Sekison and the river of blood
Hike date: November 3, 2026
For me, Mt Sekison is one of the most underrated hikes in Nagano. It’s a flank volcano on the south side of Mt Asama, but which can only be accessed from an upscale area of second homes in the exclusive resort town of Karuizawa. I often visit in late November or December, but even with the leaves in their full autumn glory there were few people on the mountain today.
The hike starts at the former post station of Oiwake-juku and involves walking for about 20 minutes along forested roads before reaching the real trailhead. Bear warnings abound and I made sure to carry spray as there have been a number of incidents reported in recent years, including one in which a trail runner was suddenly attacked. From the trailhead the path rises slowly and steadily upwards through the beautiful autumn foliage before reaching a forest road and then a narrow path. This is where you hear the sound of rushing water and the thrills begin. Before long you are looking down on the so-called river of blood, a flow of water coloured by the iron and minerals leaching out of the volcano that looms above. There then follows the waterfall of blood and the pond of blood, all of which makes you wonder whether they are overdoing the blood theme. Whatever it is, the colour of the water running off Mt Asama is like nothing I’ve seen before.
Although this is not a hike that offers many great views until the summit, I was a little disappointed that the mountain was bathed in mist the whole time. The forest was a bit spooky and I could imagine bears and other monsters emerging from the bloom. As luck would have it, the fog lifted suddenly after I reached the summit and I could enjoy fine views over the town below and back towards the dramatic rugged volcanic scenery of Mt Asama.
Check here for more information about Mt Sekison.
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