akiyoshi cave entrance chamber, japan

adventure akiyoshi akiyoshidai akiyoshido akiyoshidou ancient asia brook cave cavern ceiling chamber creek dark destination earth entrance floor formation geology green high historic honshu immense ina inagawa inakawa inside its japan japans karst known largest limestone mine monument mystic nagabuchi natural nature park quasinational river rivulet rock scenic science solutional special speleology speleothem stone stream time tourist underground view water yamaguchi