Ryusendo Cave

right|270px|thumb|Underground lake 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.

== Overview == Ryūsendō has an accessible length of 1,200 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.