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.