The tallest of Oga Peninsula’s caverns, Kankanedo Sea Cave was carved by wave erosion of rhyolite volcanic rock and land protruding from the sea. With holes opening into the sea, land, and sky (ceiling), the light shining in and the sound of the waves give it a mysterious air. It is said that in the past, an iron lock was placed on the cave’s cliff face, giving it the name Kagikakedo, or Locked Cave, which eventually became Kankanedo.