The underground lake No. 3 reaches a depth of 98 meters, while the unmapped lake No. 4 is confirmed to be at least 120 meters deep.
The water within the cave is classified as ultra-pure, ranking among the clearest in the world with a high degree of transparency.
The cave serves as a hibernation site for five different species of bats, which are protected under local conservation laws.
The cave was designated as a National Natural Monument of Japan in 1934.
The cavern temperature remains stable between 8 and 11 degrees Celsius regardless of external weather conditions.
Ryūsendō Cave is one of Japan's three major limestone caves, recognized for its series of deep, clear underground lakes. The cave system extends over 3,600 meters, though only about 700 meters are open to the public. The subterranean water is famously transparent, with some basins reaching depths of over 120 meters. The cavern environment maintains a constant year-round temperature of approximately 10 degrees Celsius. Visitors follow a set walking path that includes steep metal staircases and elevated observation platforms overlooking the azure water. The site is located in the town of Iwaizumi within the Iwate Prefecture. Scientific research indicates that the cave system is still actively expanding, with many areas remaining unexplored.
The observation deck overlooking the third underground lake, which features specialized lighting to showcase the deep blue water.
Bring a light jacket or sweater, as the cavern interior is significantly colder than the outside air.
Wear non-slip, comfortable walking shoes to navigate the steep, metal staircases safely.
Use a camera capable of high ISO settings or a tripod, as the lighting inside is dim to protect the cave environment.
Attempting to photograph the lakes using flash, which ruins the visibility of the deep water and is prohibited.
Do not touch the limestone formations, as skin oils can damage their growth; stay strictly on the designated walking paths.
