The cave was formed approximately 300,000 years ago by the eruption of the Aso volcano.
The water inside the cave is known for its high purity and is maintained at a constant cool temperature.
It holds the title of the longest underwater cave in Japan.
The interior contains a variety of limestone formations that have been submerged, preventing further surface erosion.
The site includes a museum area showcasing the history and geology of the surrounding Oita limestone belt.
Inazumi Underwater Cave is Japan's longest underwater cave, formed by the submersion of a limestone cave system after volcanic activity from Mount Aso. The cave features a unique subterranean environment where visitors walk on submerged paths through chambers filled with crystal-clear spring water. Stalamites and stalactites are preserved within the water, creating an unusual underwater landscape. The site includes a facility for cave-diving research and observation. The water temperature within the cave remains relatively constant throughout the year. The site is located in the Bungo-ono area of Oita Prefecture. Parts of the cave system remain largely unexplored, contributing to ongoing geological research in the region.
The illuminated blue-water sections where the limestone formations are clearly visible beneath the surface.
Wear comfortable, non-slip footwear as the walkways can be damp.
Bring a light jacket as the ambient temperature inside the cave is significantly cooler than the outside air.
The pathways can be narrow, so walk carefully through the submerged sections.
Attempting to photograph with flash in darker sections, as it ruins the view for others and can glare off the water surfaces.
Open year-round; check local notices for potential temporary closures due to heavy rainfall or severe weather which can affect water levels.
Do not touch the limestone formations; remain on the designated walkways at all times.
