Maja and Kuba really enjoyed playing in the park, especially under the big old oak tree. One sunny day, while they were playing hide and seek, Maja noticed something shiny in the grass. - Kuba, come quickly! - cried the excited little girl. The boy ran up and together they looked at the find. There was a small silver key lying in the grass. It was very old, a little rusty and had a strange star-like pattern engraved on the end. - I wonder what this key fits into? - asked Kuba, looking at the key from all sides. Maja looked around the park. - Maybe there's a hidden treasure chest somewhere? Or a secret gateway to a secret garden? The children began to look around. They checked under the bench, behind the bushes and around the oak tree. Suddenly they noticed something else lying at the foot of the huge tree - a round stone with a star painted on it. Mai's heart began to beat harder. She gently touched the stone, and then.... the stone moved slightly. Kuba looked at her with wide-open eyes. - Do you think this is where the key fits? - he whispered curiously. The children looked at each other, held their breath and slowly picked up the mysterious key....