The City of Wind has always had a reputation as a place full of surprises. Old townhouses with colourful facades hummed with stories as the wind swept through the narrow streets. But no one could have guessed that the greatest adventure lurked just beneath the cobblestones on which the inhabitants swept daily. On that sultry June night, Amelka was returning home from the river. The last rays of the setting sun reflected lazily in the shop windows, and the smell of lime trees mingled with the summer dust. In front of her apartment building, Kuba and Lena, two friends ready to do anything to get out of the daily routine, were already waiting. - Tomorrow is the last day of school," said Kuba, holding his skateboard under his arm. - Did you know that there are tunnels under Saperów Street? History says that long ago they were used as shelters. Now they are supposedly closed, but... - he suspended his voice and looked at Amelka with a roguish smile. Lena, slightly more sceptical, furrowed her eyebrows, but her curiosity won out over her concern: - Where did you get this information? Kuba took an old, yellowed map out of his pocket - evidently taken out of the school library or his grandfather's basement. There were strange signs on it, and a network of underground corridors stretched beneath Saperów Street. They decided to head there the next day as soon as dusk fell. They met at the western street name sign. After a while of searching and careful observation, they discovered a cast-iron manhole hidden in the bushes behind an old garage. The manhole proved heavy, but the three of them managed to open it. A musty smell wafted from inside and the steep staircase disappeared into the darkness. With torches in their hands and hearts beating faster than usual, they descended. After a few steps, the sounds of the city ceased. In front of them stretched a corridor lined with bricks. Old inscriptions glistened on the walls and echoes of the past shimmered in the side alcoves. For a long moment they walked ahead, admiring the drawings they encountered along the way and tried to decipher the faded symbols. Suddenly, Lena stopped abruptly. - Do you hear that? - she whispered. Silence. After a moment, a short, broken echo of footsteps came from somewhere deep in the tunnel. The light of their torches danced on the brick walls and the air thickened with tension. Cuba looked at his friends, trying to feign calm, but even he could not hide the tremor in his voice: - Maybe... maybe we're not alone here? A dark shape blurred from around the corner of the tunnel, and a cool gust splashed what looked like water against the brick wall. The friends froze in stillness, listening for more sounds. The light of the torches revealed a wide entrance to a side corridor, leading even deeper into the subterranean tangle....