What appears to be a doorway carved into a cliff face on the Japanese island of Yonaguni adds to evidence of ancient human habitation on the island. Sites like this have yielded charcoal likely made by human hands 1,600 years ago.

Such structures are similar to the unusual underwater formations nearby—a fact that some experts use as supporting evidence that the underwater stones are the ruins of an ancient city.

But for now neither the Japanese government's Agency for Cultural Affairs nor the government of Okinawa Prefecture recognize the remains off Yonaguni as an important cultural property, said agency spokesperson Emiko Ishida.

• More Photos in the News
• Today's 15 Most Read Stories
• Free Email Newsletter: Focus on Photography