The town of Slaughterhouse was not a place of great adventure. Usually. No one would have thought that the old bridge on Lysa had anything interesting to offer anyone other than pigeons. But for Karolina, Oskar, Magda and Bartek, it was here that something different began. They were sitting against a wall covered with a mural that, according to rumours, was painted with paint stolen from the city's arsenal. The day was cloudy, the air smelled of dust and petrol. Karolina pulled her sketchbook out from under her sweatshirt and Oskar fired up a song on the speaker that Magda hated. Bartek looked around anxiously. The bridge was old, with plaster falling off in places and metal scaffolding sticking out as if someone had tried to build armour out of it. As Oskar reached for a can of Coke, they heard a quiet creak. Not the sound of a tram or a cyclist, but something that came from under their feet. Karolina pushed aside an old rucksack and saw a small metal ring sticking out of the concrete. It attracted them like a magnet. Oskar grabbed it and pulled, but nothing happened. Bartek helped, and then all four heard a quiet click. A section of the ground suddenly lifted, revealing a stone door that would have been impossible to see from outside. They were cold to the touch, with carvings reminiscent of an old city map. Among the lines and symbols, someone had scratched out a strange inscription: 'Don't pass without a reason.' Magda looked at Karolina, expecting some logical explanation. Instead, Karolina knelt by the door and pressed her hand against it. They shook gently, as if responding to her touch, and then a light appeared - cold, blue and unreal. In the silence, broken only by the distant hiss of tyres, they decided they would try to open it. Bartek, always the first to act, moved his hand over the carvings, looking for some hidden mechanism. Then the door began to open slowly, revealing darkness and a staircase that disappeared somewhere deep under the bridge. No one spoke a word. The light from inside pulsed in rhythm with the beating of the hearts of all four of them. Karolina looked at them all: - Shall we go? - She asked quietly, and her voice echoed off the walls. At that moment, in the blinding darkness beneath the stairs, something moved, there was a dragging sound that could hardly be attributed to anything any of them knew