Julka sat on the steps of the old, long-closed school and watched intently as the sun slowly disappeared behind the darkening trees. Next to her stood Kuba - a short, red-haired boy with a head full of crazy ideas - and Lena, who loved to break all the rules. It was going to be an ordinary holiday, until they stumbled upon a black book hidden in a creaky wardrobe in the corridor. "Look! Here's a map," said Cuba, turning a yellowed page. Drawn on the page were a staircase, an underground corridor and something that looked like a closed door with a strange symbol - an eye inscribed in a circle. Julka felt a shiver run down her spine. Hidden from the sight of their neighbours, the three of them sneaked into the school basement after dark. Every step echoed through the cold walls. Lena found a loose slab in the floor. Beneath it stretched a tunnel, as if created especially for them. They walked on all fours a dozen metres until they saw a door. It was old, covered in a thin layer of silver dust. Above the doorframe was engraved the same symbol as on the map. When Lena touched the handle, they felt a slight blast of cool air and heard quiet whispers, the words of which merged into incomprehensible sentences. They wondered whether to retreat, but curiosity won out. The door opened slowly, revealing a narrow, dusty corridor, at the end of which a bluish light smouldered. Strange shadows appeared on the walls, as if hundreds of eyes were following their every move. Suddenly, the ground beneath their feet began to tremble slightly, and from the abyss of the corridor came a prolonged, intriguingly familiar cry: "Help us..." Julka turned to face her friends. She knew they had to decide whether to take a step forward - into the unknown world that was just opening up to them - or turn back before it was too late....