Cuba and Lena's school was as old as the world, and the cellar underneath was even older. Legend had it that it once housed a vault, but none of the pupils took the stories seriously. Until now. It all started when, during a rainy break, Lena found a metal trapdoor under the stairs, masked by dust and cobwebs. She quietly called out to Kuba, who happened to be moving down the corridor on his knees, pretending to be a police dog. - Look, this was never here, was it? - whispered Lena, touching the cold metal. - Maybe it's just that nobody noticed it? - replied Cuba, trying to sound brave, although curiosity shone in his eyes. They carefully lifted the flap with a ruler, and underneath it a narrow descent appeared. It smelled of dust, old paper and something else - like the air of a hundred years ago. Instead of returning to her lessons, Lena pulled a torch from her backpack (she was always prepared for surprises) and Kuba squeezed inside first. They descended slowly, suppressing nervous giggles. The walls were of brick, overgrown with strange lichen that glowed in the dark. Suddenly they stopped in front of an old wooden door. On them hung a sign: DO NOT OPEN - THREATEN TO SECRET. - Oh no, this is definitely a trap! - Lena whispered fascinated. But curiosity was stronger than fear. Kuba put his hand on the door handle. At that moment, a soft, melodious whisper came from behind the door.... And then... the door began to open slowly.