The beautiful stalactites and stalagmites were created over 175,000,000 years. At the entrance of the cave is the ruins of a Yayoi period cave dweller site. The Yayoi era earthenware, covered in calc-sinter, is of global importance. In 1934 the site was designated as a National Natural History Site and National Historical Site. In addition to the approximately 1 km Tourism Course, you can squeeze through the narrow spaces together with a navigator and ascend a wooden ladder on the Adventure Course (reservation required). ON the second Sunday of each month (except August), the lights in the 400 meter stretch from the entrance is turned off from 10:00-11:00, and you can explore the cave with flashlights on the Dark Tour.