Ignacy Lukasiewicz School looked as dull as ever that morning. Between the hum of conversations in the corridors and the calls of the teachers, the three friends - Maja, Adam and Kuba - were lurking at the entrance to the ground floor bathroom. It was here, during the last lesson, that Adam noticed something unusual: there was a small metal hatch in the floor under the sink. Naturally, their curiosity was stronger than common sense. After a quick reconnaissance - once they had made sure no one was watching them - Maja slid her hands under the hatch and lifted it surprisingly easily. The hatch led into a narrow tunnel with a pleasant smell of... mint? Intrigued, they crawled inside, using the torch on Kuba's phone. The walls of the tunnel shone with a pearly white sheen, as if they were made of porcelain. - 'Something like in a toothpaste advert,' Maja joked, but Adam felt increasingly strange, as if the tunnel was watching them. The further they walked, the more unusual details they noticed. In some places, the walls were covered with strange, soft toothbrushes, and in places, thin threads - resembling dental floss - dangled. Eventually the tunnel widened and the friends stood in front of a huge gate made of shiny white tiles. Above the gate was the inscription: "City of Teeth - Admission only for those who know the Secret of Brushing". Before they had time to think of what to do next, they heard a deafening sound on the other side of the door and someone's footsteps....