Onioshidashi Park
📍 Gunma, Tsumagoi
A black lava field below Mt. Asama, frozen mid-flow by the catastrophic 1783 eruption, with walking paths winding through the rock to a hillside memorial temple.
Onioshidashi Park (鬼押出し園, Onioshidashi-en) preserves one of the most dramatic lava fields in Japan: a stretch of rugged black rock, roughly 5km long, left behind when Mt. Asama’s catastrophic 1783 eruption sent lava and pyroclastic material pouring across the landscape and cooling in place. Walking paths wind between the formations to a hillside temple with views back over the whole field.
Why It’s Interesting
The name translates roughly to “where the demons pushed the rock out” — the eruption was violent enough that witnesses at the time described it in those terms, and the landscape still looks the part: block-like, jagged lava piled across more than a thousand hectares, with Mt. Asama itself rising behind it. At the center of the park stands Asama Kannon-dō, a branch temple of Tokyo’s Kan’ei-ji, built in 1958 to honor those who died in the eruption — a quiet, deliberate counterpoint to the raw geology around it.
Best Time to Visit
The park is open year-round (8:00–17:00, last admission 16:30). From mid-May, alpine flowers — Iwakagami, Tsugazakura, and other high-altitude species — bloom directly out of the cooled lava, and autumn brings clearer long-distance views of Mt. Asama and Mt. Shirane from the temple’s overlook.
Getting There
There’s no direct train or bus stop, so a car is effectively required. The park sits at around 1,300m elevation in Tsumagoi Village, roughly 20 minutes from Kusatsu Onsen and 30–40 minutes from Karuizawa — both make it a natural stopping point on the drive from Shiga Kōgen back toward Tokyo via the Joshin’etsu Expressway.
🐿️ Cinnamon was here
Field report
Ghost popsicle asked what's worth seeing on the drive back toward Tokyo, and this is the one I kept circling back to — it sits almost exactly on that road, past Kusatsu, no detour required.
The lava came down in 1783, one violent push from Mt. Asama, and it never got the memo to melt back into anything gentle — it just sits there, block on block, silent and enormous. I hopped the marked paths between the rock rather than the rock itself, which the humans around me were sensible enough to do too, and ended at a little temple built on a rise for the people the eruption killed, with the whole black field and the mountain itself laid out below it.
Other visitors say mid-May is the trick — that's when tiny alpine flowers start pushing straight up out of the cracks in the rock, which sounds like exactly the kind of stubbornness I respect. Even without the flowers, it's a strange, sober, worthwhile hour on the way home.
— Cinnamon 🐿️
📸 Cinnamon's camera roll
Snapshots from our very good boy on the road.
Where it is
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