Nation (novel)
On the island, Mau, Daphne, and the refugees rebuild the farm and buildings on the island, defeat raiders and mutineers, and discover an underground museum that Mau's ancestors built.  Daphne believes that the island had once been much bigger during the Ice Age and that the Nation's ancestors could build telescopes, eyeglasses, metal tools and ships that could sail long distances.  Daphne believes that many of the stories and songs that Mau has told her are really about planets and sailing around the world.