eons of flow marked in akiyoshi cave

adventure ages akiyoshi akiyoshidai akiyoshido akiyoshidou ancient architectural asia brook cave cavern chamber creek dark destination earth element flow formation geology green historic honshu ina inagawa inakawa inside japan japans karst largest limestone mine monument mystic nagabuchi natural nature park quasinational record river rivulet rock scenic science solutional special speleology speleothem stone stream time tourist underground view wall walls water yamaguchi