Inazumi Underwater Cave (稲積水中鍾乳洞) 稲積水中鍾乳洞
The submerged passage is over 1,000 m long; the water, 30 m deep in 1976, is now only 7.
In Bungo-Ōno, the Inazumi cave is Japan's most extensive cavity with submerged stalactites: the limestone formations were created in a dry environment and later submerged by water. It was first explored in the spring of 1976 by a diving club from Saiki, which surveyed over 500 metres in the submerged part alone; development began in the summer of the same year, with scientific surveys until autumn 1977. After renovation it reopened in August 2005. The water depth, once 30 metres, is now only 7 metres thanks to drainage work; surveys in 2014 confirmed over 800 metres of submerged passages with branches, for a total length of over 1,000 metres. Since March 2019 the cave has offered the first diving/snorkelling experiences in a submerged cave in Japan. In January 2021 it appeared in the opening sequence of the anime Sazae-san.
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