Inazumi underwater Cave

This rare underwater cave was created when limestone caves formed 300 million years ago during the Paleozoic Era were submerged in water by the eruption of Mt. Aso 300,000 years ago. At approximately 1 km in length, it is the longest underwater limestone cave in Japan, and its research continues to this day.

The caves are divided to the two sections, the new caves and the underwater caves. You can see fascinating natural artwork created over a long period of time, including the “Bell holes” with a ceiling carved like many bells, the magical “Ryugujo” cave illuminated with blue lights, and the “Jigen no Fuchi” cave where the rock formation under the water is clearly visible. The temperature in the interior of the caves remains 16 Celsius all through the year. It is cool in summer, and warm in winter, making for naturally comfortable spaces.

There are equipment rentals and tour service for snorkel and scuba diving (requires pre-booking and additional fees).

The Inazumi Underwater Cave　is located over a large area, and there are many other sites visitors can enjoy along with touring the underwater caves; sites include the Inazumi Ascending Dragon Kannon, the tallest Buddhist statue in Oita Prefecture, and "Showa Time Trip Romanza," a recreation of streets from the Showa period.