Jomon Tennen Onsen; Shiraku no Yu

Setagaya, Tokyo, Japan

Location: Setagaya, Tokyo, Japan
Water type: bicarbonate, calcium-rich
Temperature: 40 °C
pH: 8

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.

BicarbonatesSodiumCalcium

Jomon Tennen Onsen Shiraku no Yu is a natural hot spring facility whose name invokes the prehistoric Jomon culture — Japan's ancient hunter-gatherer civilization that flourished across the archipelago for over ten thousand years before agriculture arrived — evoking the primordial, unmediated connection to the earth's warmth that thermal bathing represents at its most elemental. The bicarbonate, calcium, and simply mineralized waters offer a therapeutically balanced composition: alkaline bicarbonate for skin softening and detoxification, calcium for muscular and skeletal support, and the clean, uncomplicated warmth of lightly mineralized waters for general well-being and profound relaxation. 'Shiraku no Yu' — conveying modest ease and quiet pleasure — reflects a philosophy of accessible, uncomplicating comfort in thermal bathing that honors the dignified simplicity of everyday Japanese wellness culture.

Insider tip — Jomon Tennen Onsen Shiraku no Yu draws natural bicarbonate and calcium-rich spring water from deep Jomon-era geological strata beneath the Setagaya ward of Tokyo, a remarkable feat in one of the world's most urbanized districts. The dark, tea-colored water signals high organic mineral content prized for skin softening and relaxation. Late-night bathing is popular with Tokyo residents unwinding after long commutes, with the facility often open past midnight. The ancestral geological layers lend each soak a quiet connection to the city's prehistoric past.

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