Chatsubomigoke Park

Published: Aug 11, 2026

Updated: Aug 11, 2026

chatsubomigokemossnatural monumentNakanojoformer mine

Representative image — not a photograph of this location.

At the far western edge of Nakanojo, in a basin formed by eruptions of Kusatsu-Shirane, warm acidic springs seep out of the ground and a moss called chatsubomigoke grows on them in a continuous glowing green mat. Almost nothing tolerates water this acidic, which is exactly why the moss has the place to itself. The hollow it fills is called Ana-Jigoku, 'hole hell', a name given long before anyone came to admire it.

The site is also an industrial ruin. This was the Gunma Iron Mine, the country's largest source of limonite, worked until it closed in 1966 — and the iron ore was being produced by the same acidic water and iron-fixing bacteria that keep the moss alive. That combination of a rare biological community and an active ore-forming process got the site designated a national natural monument in 2017. A boardwalk loop takes you around and down into the hollow; the moss is at its most saturated after rain and in the low light of early morning.

Essential Information

Opening Hours

8:45 AM – 4:00 PM | Last admission 3:30 PM (April–September), 3:00 PM (October–November)

Closed: Closed December–late April (winter closure; exact dates shift with snowfall)

Entrance Fee

¥600 adults | Free for elementary school age and under

Best Season

Late April–November (open season) | Late October–early November for autumn colour against the green moss

Visit Duration

60–90 minutes

Getting There

Access Information

13-3 Iriyama, Nakanojo. Car strongly recommended — around 40 minutes from Kusatsu Onsen. Admission ¥600 for adults, free for elementary school age and under. Open 8:45 AM – 4:00 PM, with reception closing 3:30 PM April–September and 3:00 PM October–November. Open late April to the end of November only; closed for winter. Free parking for about 50 cars. Phone 0279-95-5111.

Insider Guide

Premium

**Timing decides how green it looks.** The moss reads as vivid green in soft light and washes out in hard midday sun. Early morning after overnight rain is the best combination; the boardwalk sections nearest the seeps hold mist well into the morning in autumn. **Combine with Kusatsu, not with Tokyo.** This is around 40 minutes by car from Kusatsu Onsen and awkward to reach any other way. Treating it as a half-day loop out of Kusatsu — park, moss, then back for an afternoon bath — is how it actually fits into a trip. **Late October is a double season.** The surrounding slopes turn while the moss stays green, and the contrast between autumn colour and the fluorescent green hollow is the reason most Japanese photographers come. That is also the busiest window; weekday mornings are noticeably quieter. **Reception closes well before the park does.** Note the two different times: last admission is 3:30 PM in the warmer months and drops to 3:00 PM from October. Turning up at 3:45 PM in November means being turned away. **Read the mine, not just the moss.** Interpretive signage covers the Gunma Iron Mine and why the ore and the moss are the same phenomenon. It is a genuinely unusual thing to be able to see — a working geological process rather than a preserved one.

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