Ryūsendō is one of Japan's three largest limestone caverns. It is located in the town of Iwaizumi, Iwate Prefecture, in the Tōhoku region of northern Japan. Ryūsendō has an accessible length o…Ryūsendō is one of Japan's three largest limestone caverns. It is located in the town of Iwaizumi, Iwate Prefecture, in the Tōhoku region of northern Japan. Ryūsendō has an accessible length of 1200 meters, making it the 62nd longest in Japan; however, its depth of 249 metres 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, 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, and the fourth of which has a depth of over 120 metres. 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.