Complete explanation of differences in water quality, history, access, and 2025 trends
Kusatsu, Arima, and Gero are known as "Japan's Three Famous Springs" (Nihon Sanmeisen). Their reputation was established centuries ago by the Confucian scholar Hayashi Razan during the Edo period, and they remain iconic to this day. However, their characters are surprisingly different. This guide thoroughly compares these three hot spring areas.
Part 1 : This article
Chapter 1: Extreme Differences: "Acid vs. Salt vs. Alkali"
Chapter 2: Differences in Urban Design
Part 2 :
Chapter 3: [Access & Logistics] Ease of Travel (2025 Context)
Chapter 4: Take-home Experiences
Chapter 1 : Extreme Differences: "Acid vs. Salt vs. Alkali"
The biggest difference lies in the chemical properties (pH value and components) of the water.
Kusatsu Onsen: The Strong Acidic "Curing Water"
- Quality: Acidic / Sulfur-Aluminum-Sulfate-Chloride Spring
- pH Value: Approx. 2.1 (Strong Acid)
- Features: Known for its powerful bactericidal power capable of dissolving a 5-inch iron nail. It is said to "cure everything except lovesickness" and is effective for cuts and skin diseases.
- Sensation: A tingling, stimulating sensation on the skin. Leaves you feeling refreshed after bathing.
Arima Onsen: Multi-component "Warming Water"
- Quality: Iron-Sodium-Chloride Strong Salt Spring (Kinsen / Gold Spring), Carbon Dioxide / Radioactive Spring (Ginsen / Silver Spring)
- pH Value: Kinsen is neutral to weak acid (approx. 6.3), Ginsen is weak acid.
- Features: A rare complex spring containing 7 of the 9 main components designated as therapeutic springs by the Ministry of the Environment.
- Gold Spring (Kinsen): Rich in iron and salt, turning reddish-brown upon contact with air. Provides excellent heat retention and moisturizing effects.
- Silver Spring (Ginsen): Clear and colorless. Contains carbon dioxide (promotes blood flow) and radon (boosts immunity).
Gero Onsen: Alkaline "Beauty Water"
- Quality: Alkaline Simple Hot Spring
- pH Value: Approx. 9.2 (Alkaline)
- Features: The high alkalinity acts like natural soap, removing old keratin (dead skin cells) through a natural peeling effect.
- Sensation: A distinct slippery and smooth texture (nuru-nuru). Gentle on the skin, making it suitable for everyone from children to the elderly.
Chapter 2 : Differences in Urban Design
Kusatsu Onsen: "Mortar-shaped Theater City" centered on Yubatake
- Symbol: Yubatake (Hot Water Field). A massive source facility where approx. 4,000 liters of hot water gush out every minute. The steam and nighttime illumination create a fantastical atmosphere.
- Landscape: The town spreads radially from the Yubatake at the bottom of the valley. The path leading to "Sainokawara Park" is lined with souvenir shops, creating a perfect density for strolling in yukata.
Arima Onsen: "Labyrinthine Hideaway" of Alleys and Slopes
- Symbol: Nene Bridge / Taiko Bridge and various Thermal Sources (e.g., Tenjin Source) scattered throughout the town.
- Landscape: Located in a canyon of Mt. Rokko, the town is built on steep slopes with narrow, winding alleys. The historic streetscape of "Yumoto-zaka" is filled with emotion, and steam rises from pipes and sources tucked between buildings.
Gero Onsen: Open "Riverside" Resort
- Symbol: Hida River & Gero Bridge, Chaplin Statue, and Hayashi Razan Statue.
- Landscape: The ryokan (inn) district stretches along the wide Hida River, offering an open and airy view. The "Funsenchi" (riverbed pool) was once a famous open-air bath but is now exclusively a footbath.
Part 1 : This article
Chapter 1: Extreme Differences: "Acid vs. Salt vs. Alkali"
Chapter 2: Differences in Urban Design
Part 2 :
Chapter 3: [Access & Logistics] Ease of Travel (2025 Context)
Chapter 4: Take-home Experiences
