A Long History as a Sacred Place
Since ancient times, Himesaka Limestone Cave has been known as Ohoraana, meaning “Great Cave,” and worshipped as a sacred place where the divine resides. According to tradition, in 802, during the Daido era, the Buddhist monk Kukai, also known as Kobo Daishi, visited the area and invited the deities Izanagi and Izanami to be enshrined here as guardian deities of Sanbioji Temple. This event is regarded as the origin of Himesaka Limestone Cave Shrine.
The shrine has long revered the limestone cave itself as its sacred object of worship. This ancient spiritual tradition continues to form an important part of the area’s cultural heritage.
Stone Stalactites as Precious Medicinal Materials
Historical records also associate the cave with the use of mineral formations for medicinal purposes. According to the *Nihon Sandai Jitsuroku*, an official chronicle of Japan, in 859, during the Jogan era, an imperial court official named Izumo no Asomi Minetsugu was dispatched from the capital to collect a sacred mineral known as sekishōnyū, or “stone stalactite,” from the cave.
This mineral was apparently prized as a rare and valuable medicinal substance among the upper classes of Japanese society at the time, highlighting the cave’s historical significance beyond its religious role.
Geological Features and Cave Structure
One of Japan’s Major Limestone Caves
Himesaka Limestone Cave is an enormous fissure-type limestone cave extending for more than 2,128.5 meters, with a vertical difference of 184 meters. It is recognized as one of Japan’s major cave systems and contains underground lakes, vertical shafts, and a variety of secondary mineral formations.
The temperature inside the cave remains relatively stable throughout the year, generally ranging from 12°C to 14°C. This creates a naturally cool underground environment, quite different from the conditions outside.
The Mysterious Pool of the Gods
For many years, the deepest known part of Himesaka Limestone Cave was believed to be a place called Kami no Ike, or the Pool of the Gods. In 1971, however, an exploration team led by Akira Shibata managed to pass through the pool during a period of low water and discovered a previously unknown section of cave extending another 700 meters beyond it.
This discovery attracted the attention of cave explorers and established Himesaka Limestone Cave as a destination associated with challenging underground exploration. The discovery also revealed that the cave system extended much farther than previously understood.
Exploring the Cave’s Internal Passages
Three Cave Entrances
Himesaka Limestone Cave has three entrances. The First Entrance, approximately 20 meters high, lies to the southwest of Himesaka Limestone Cave Shrine. The other two entrances, known as Hoshiana and Oana, are vertical shafts. Hoshiana is now difficult to access because of dumped materials obstructing the passage.
From the Pool of the Gods to the Deepest Chamber
Approximately 500 meters from the First Entrance, visitors reach the area of the Third Entrance, known as Oana, beyond which lies the Pool of the Gods. The pool is normally submerged, making passage difficult except during periods of low water.
Beyond the pool, the cave passage turns south and continues toward the deepest section, passing through three points equipped with ladders. At the end of this route lies an underground lake whose mysterious appearance has long fascinated explorers.
The Enigma of the Underground Lake
The underground lake in the deepest part of the cave measures approximately 30 meters wide and 25 meters long, with a depth of around 35 meters. The water is extremely cloudy, with visibility of less than one meter.
The water moves very slowly, and its ultimate destination remains unclear. These unusual characteristics have helped preserve the lake’s mysterious reputation and add to the fascination surrounding the cave’s unexplored depths.
Exploration, Tourism, and Safety
A Challenging Destination for Cave Enthusiasts
With its dramatic underground formations, deep shafts, and hidden lake, Himesaka Limestone Cave has attracted cave explorers and visitors interested in subterranean environments. However, the cave presents serious hazards, particularly in areas beyond the Pool of the Gods, where specialized equipment and extensive precautions would be essential.
Serious accidents have occurred in the cave, prompting authorities to strengthen safety measures and restrict access.
Entry Restrictions Following a Serious Accident
In 2008, an accident occurred at the underground lake in the deepest section of the cave. Safety measures were strengthened afterward. Because of the history of serious accidents, Himesaka Limestone Cave is currently subject to an entry ban among the limestone caves in Niimi City.
Although its natural and historical significance remains considerable, the cave should not be approached as an ordinary tourist attraction. Visitors and cave enthusiasts must respect the access restrictions and prioritize safety. The cave’s sacred heritage and geological importance can still be appreciated through its history and connection with Himesaka Limestone Cave Shrine, without entering the restricted underground passages.
A Sacred Landmark with Geological and Historical Significance
Himesaka Limestone Cave is remarkable for the way its natural features intersect with centuries of religious tradition. Revered as a sacred place since ancient times, it later became known for its mineral formations, extensive underground passages, and the discovery of its hidden lake.
Although entry is currently prohibited because of safety concerns, its geological scale, historical references, and enduring spiritual significance make it an important part of the natural and cultural heritage of Niimi City and the Atetsudai region of Okayama Prefecture.