Wikipedia
is one of Japan's three largest limestone caverns, located in Iwaizumi, Iwate Prefecture, Japan. Ryūsendō has an accessible length of 1200 meters, making it the 62nd longest in Japan; however, its depth of from the entrance to its lowest point is the 5th deepest in Japan. The total confirmed length of the cave is currently , although the cave may extend much further. Further exploration has been banned following a fatality in December 1968. The cave system includes at least four underground lakes, the third of which has a depth of , and the fourth of which (not accessible to the public) has a depth of over . The cave system is also home to colonies of Greater horseshoe bat, Eastern long-fingered bat, Brown long-eared bat and Hilgendorf's tube-nosed bat as well as Microbats.
Ryūsendō was designed a Natural monument by the Japanese government in 1934. The caves were opened to the public in 1967. Its underground lake system was designated one of the “100 Famous Springs of Japan” in 1985 by the Ministry of the Environment.。 The adjacent caves nearby were discovered in 1967. It claims to be the “first natural cave science museum in the world”, and contains displays of earthenware and stoneware discovered in 1967, together with displays on the geology of the main Ryūsendō caverns.