In late June they reach the volcano, which has three craters. According to Saknussemm's message, the route to the earth's center is via the crater that's touched by the noontime shadow of a nearby mountain peak, Scartaris, just before the end of June. But at that point the weather proves too cloudy for any shadows, and Axel hopes this will force his uncle to abandon the project and go home. Alas for Axel, the sun finally comes out, and Scartaris's shadow indicates the correct crater.