The cave is estimated to be approximately 30 million years old based on geological studies of the limestone formations.
The temperature inside the cave remains consistently around 10-12 degrees Celsius year-round.
Portions of the cave were discovered by local residents while mining for limestone in the early 20th century.
The cave contains a 'C course' that is essentially a wild-caving experience involving significant physical exertion.
The site is one of the few limestone caves in Japan where visitors can traverse the actual underground water flow.
Irimizu-shōnyūdō is a natural limestone cave system in Tamura, Fukushima, known for its challenging exploration routes and subterranean river. The cave is officially designated as a Natural Monument by the Japanese government. Visitors can choose between three exploration courses: Course A is the standard walking route, while Courses B and C require crawling through narrow, water-filled passages. The cavern maintains a constant internal temperature throughout the year, regardless of external weather conditions. It is home to diverse rock formations, including stalactites and flowstones. The environment is notably humid, and the interior is largely unmodified to preserve its rugged character. Natural inhabitants include various species of cave-dwelling bats.
The entrance area where the light from the outside meets the dark opening of the cave.
Rent the provided rubber boots and headlamps, as the ground is perpetually wet and muddy.
Wear clothing that you do not mind getting dirty, especially if you choose the advanced courses.
Bring a change of clothes and a towel, as you are likely to get wet regardless of the course selected.
Do not wear sandals or open-toe shoes; sturdy footwear is essential for safety.
Closed on specific winter dates and occasional maintenance days; check local official notices before arrival.
Do not touch the stalactites, as oils from human skin can halt their growth process.
