One summer afternoon, as the sun began to hide lazily behind a line of old oak trees, Marysia, Franek and Igor were roaming around the woods on the outskirts of the town of Shady. They had always loved to wander along paths where the leaves whispered under their shoes and the sun's rays danced on the bark of the trees. On this day, however, everything seemed different - the air had a taste of adventure, and the wind whistling between the branches carried with it something uncanny. Marysia, who always had a magnifying glass and a notebook in her pockets, suddenly stopped at an old, mossy trunk. She squatted down and raised her hand, pointing to something under the leaves. - Look! - She whispered excitedly. - These are no ordinary footprints. Franek, the eldest of the group and a real expert on forest tracks, looked at the mysterious prints. They were large, with three fingers, and around them were tiny, shiny pebbles. The whole thing formed a line, as if someone or something had led them straight into the forest. - Have you ever seen anything like this? - asked Igor, who had an imagination so vivid that he could find a dinosaur on the school playground. - I don't think so... - replied Franek, wrinkling his forehead. - Do you think we can see where they lead? Marysia had already set off on the trail of footprints. The deeper they went into the forest, the quieter it became around them. Birds' trebles gave way to a strange silence, as if everyone had become speechless. They shuffled between bushes and trees, feeling more and more excited. The footsteps turned abruptly, climbed hills and then descended gently into a valley neither of them had seen before. At the bottom of the valley, a huge boulder awaited them, quite overgrown with lichen and ivy. But what caught their attention was a small indentation in the stone, resembling a gate. It was dark inside, and there was a sound coming from within - quiet, though distinct, as if someone was playing an invisible harmonica. Suddenly, Franek noticed that on the ground around the entrance lay old, rusty keys and a piece of paper with a barely visible drawing of a clock without hands. - Do you think we should go inside? - Marysia asked in a whisper. At that moment the ground shook beneath their feet and there was a deafening echo, as if something or someone was waiting for their decision....