Kawarage Jigoku is Yuzawa's harsher geothermal landscape: pale, bare slopes, sulfur in the air, and steam rising from a mountain that has long been treated as a spiritual "hell." It feels very different from the green gorge at Oyasukyo, and that contrast makes the detour worthwhile.
Nearby Kawarage Oyutaki is the stranger prize, a hot-spring waterfall where heated water drops into a natural bathing pool. The bathing season is short, usually midsummer into early autumn, and the mountain road closes in winter. Bring a swimsuit and check access before setting out.