Ryūsendō (龍泉洞) 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 249 metres (817 ft) from the entrance to its lowest point is the 5th deepest in Japan. The total confirmed length of the cave is currently 3,631 metres (11,913 ft), 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 98 metres (322 ft), and the fourth of which (not accessible to the public) has a depth of over 120 metres (390 ft). The cave system is also home to colonies of Greater horseshoe bat, Eastern long-fingered