AT A GLANCE
Why go?
Yorunoike (夜の池), meaning "Night Pond," is a small, spring-fed lake tucked into the forested foothills of Mt. Kasatori in Nagawa Town, eastern Nagano Prefecture. At just 0.9 hectares, it is a quiet, mirror-still body of water that seems to have appeared from nowhere — and according to legend, it literally did, materializing in a single night.↗
What makes Yorunoike remarkable is not its size but its strangeness. A small floating island sits at its centre, reachable only by a short wooden bridge; the water is so clear that iwana (char) can be seen swimming below the surface; and the pond's very existence is rooted in a dramatic geological story told in supernatural terms. Designated as a Place of Scenic Beauty by the town since 1971, it remains one of Nagano's best-kept secrets — a pocket of mystery along a country road that rewards the curious traveller.↗
A Pond Born in a Single Night
Geologists would call Yorunoike a landslide-dammed lake. The accepted natural explanation is that during a prolonged rainy season, a section of the hillside above the pond gave way, and the resulting depression quickly filled with rainwater and underground springs. Local memory preserves this event with remarkable precision: residents say the pond appeared overnight after a landslide on the flank of the mountain above the village of Nonoiri.
