In the Mediterranean Sea off the coast of Libya, there’s an area local fishermen call “Turtle Island.” It’s real enough, but you’d be foolish to try to sail there. The island is never in precisely the same place, and it changes size from one minute to the next. In fact, you never know when its gleaming shore might disappear altogether, because it’s made up entirely of the half-exposed shells of basking loggerhead sea turtles.