The Ignacy Domeyko School had long, still untold stories. Old walls, rumours of past events and cellar corridors that were not mentioned in any official plan of the building - all this stimulated the imagination, especially during long, quiet evenings. Natalia, who has always been enchanted by architecture and urban planning, once found by chance a strange fragment of the school plan in the library archives. There was an outline of small rooms under the assembly hall, connected by a narrow passageway - never before seen on an actual plan. For weeks she whispered about it to her closest friends - Charles, who had a passion for history, and Victor, constantly looking for inspiration for his stories. One autumn afternoon, when the rest of the students had long since left school, the three of them decided to check if the underground corridor really existed. With old torches, telephones and a plan in hand, they descended the creaking stairs leading to the cellars. The air here was heavy, smelling of dust and old paint. They made their way around several warehouses of unnecessary equipment until they finally reached a dead end where there was a narrow, half-open door behind a rusty cupboard. Charles pushed it open with surprising ease. It was dark inside, yet Natalia entered first, followed by the others. A corridor stretched before them, lit by a single, barely smouldering bulb. The silence was only broken by their quiet footsteps and the echoing sound of water dripping from old pipes. After a few minutes of walking, they came upon another door, this time heavy, steel, with unusual symbols carved around the lock - geometric shapes arranged in something like a circle, full of bizarre signs neither of them had ever seen before. Victor, fascinated, ran his fingers over the engraving while Natalia tried to decipher whether the symbols reminded her of any familiar architectural signs. Charles peeked through a small gap between the door and the doorframe, but darkness prevailed further on. - What do you think this is? - Karol whispered. - Maybe someone hid something here at some point, maybe it leads to some sort of shelter? - suggested Natalia, not taking her eyes off the lock. Viktor leaned over to take a closer look at the circle of symbols. Then, suddenly, one of the lights flickered and the steel door began to creak slowly, as if someone - or something - was trying to open it from the other side. All three held their breath. They waited in uncertainty, not knowing whether to take a step back or take a chance and see what was hidden on the other side of the door. A quiet noise sounded, as if a breath of wind, and the hitherto closed passage began to radiate a pale blue light....