Shortlisted for the 2018 4-11 Picture Book Awards Is Petra a mountain? An egg? Who knows! She s a rock and this is how she rolls. Petra is a mighty mountain that can t be moved by the wind or time. Or so we think until we discover that she s actually something even more astonishing. Petra has the potential to be anything an island, an egg, even an elephant thanks to her lively imagination.