It's a natural spring in Chibu associated with a local guardian deity. The spring is considered sacred and its water is traditionally used for spiritual purification and possibly drinking.
Many such springs host annual festivals, but I don't have specific information about events at this particular spring. Contact local tourism offices for current festival schedules.
Many guardian deity springs have a small shrine nearby for worship and offerings. Whether this specific spring has one would need to be confirmed through local sources or a visit.
Bow before approaching, rinse your hands and mouth if there's a purification basin, speak quietly, don't litter, and if making an offering, bow before and after. Avoid stepping directly on sacred areas or touching shrine structures.