The content of this product is provided by machine translation and may not reflect the actual information, please take this into consideration before booking.-What is Inazumi Underwater Cave?- The Inazumi Underwater Cave in Bungo-Ono City, Oita Prefecture, was formed 300 million years ago during the Paleozoic era, and was submerged by the great eruption of Mount Aso 300,000 years ago, giving it its current shape. This is a rare underwater cavern in the world, where you can see many underwater stalactites, coral stones, bell holes, helictites, and more. The temperature inside the cave is 16 degrees all year round, so you can enjoy sightseeing in a cool space in the summer and a warm space in the winter. -Business hours- 9:00-17:00 (extended hours in summer) *Open all year round.