Hashiri-yu is one of the three ancient hot springs of Japan, known as the 'Zuisen' or 'auspicious springs'.
Historical records from the 'Azuma Kagami' mention the spring's activity as early as the 12th century.
The spring water is classified as a calcium-chloride spring, traditionally noted for its high mineral salt content.
The cave environment maintains a high level of humidity and geothermal heat throughout the year.
The water temperature at the source remains consistently hot enough to reach near-boiling points, requiring cooling systems before use in local baths.
Hashiri-yu is one of Japan's oldest hot-spring sources, located within a natural cave at the base of Mount Izusan in Atami. The name translates to 'running water,' referring to the historic observation of water surging from the cliffside toward the ocean. It is officially designated as a tangible cultural property by Shizuoka Prefecture. The site features a concrete-lined tunnel that allows visitors to walk directly into the steam-filled cave to view the geothermal activity up close. The spring water flows at a temperature of approximately 70 degrees Celsius, discharging about 7,000 liters per hour. It has been documented in historical records dating back over 1,200 years, making it a focal point of Atami's long-standing reputation as a spa destination.
The entrance tunnel looking toward the steam-filled interior cave chamber.
Wear light clothing, as the humidity and heat inside the cave are significant.
Use caution when walking, as the floor inside the cave can be slippery due to steam condensation.
Bring a small towel to wipe away condensation if you wear glasses.
Do not attempt to touch the water flowing from the source, as it is hot enough to cause burns.
No bathing is permitted inside the cave source; respect the signage as it is a protected historical site.
