Kashi Onsen

Minamiaizu, Fukushima, Japan

Location: Minamiaizu, Fukushima, Japan
Water type: silica, calcium-rich
Temperature: 40 °C
pH: 7.2

Water profile

Thermicity

Sedative

40 °C

LowHigh

Relaxing — deep, immediate muscle release.

Mineralisation

Restorative

LowHigh

Loaded with major ions — the essential minerals (Ca, Mg).

Buoyancy

Standard buoyancy

LowHigh

Soft water — natural, classic buoyancy.

SiliceSodiumBicarbonates

Kashi Onsen takes its name from the kashi oak—a hardwood tree known in Japan for its exceptional durability, strength, and deep-rooted character—a name that suggests a spring of long-established, enduring quality in the landscape it inhabits, as steadfast as the oak itself. The triple mineral profile of siliceous, calcareous, and simple waters creates a bath of layered therapeutic character: silica softens the skin, calcium builds warmth retention within the body, and the gentle alkaline base makes the combination accessible for extended daily soaking across all seasons. This mineral richness, combined with the oak's symbolism of strength and permanence, gives Kashi Onsen a character of sustained, deep nourishment rather than the fleeting intensity of more dramatically volcanic springs.

Insider tip — Kashi Onsen in the mountains of southern Fukushima combines silica-rich and calcium-bearing waters in a blend renowned for its remarkable skin-softening effects — locals call it bijin-no-yu, or beauty water. The silica content coats the skin in a silky film detectable immediately upon emerging from the bath. Set in a deep river gorge surrounded by old-growth forest, the onsen is accessible only via a winding mountain road that discourages casual visitors, preserving its tranquil character. Autumn transforms the canyon walls into vivid natural tapestries of maple and oak.

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