Cuba has always liked to seek adventure where others have only seen the dull streets and old cobblestones of their town square. It was supposed to be an ordinary Friday evening, but when he met up with Ola and Tymon, something hung in the air. They sat by the fountain, considering what interesting things they could do tonight. - 'Did you hear that in the old basement underneath the bookshop they recently discovered some kind of blinded corridor?' - Ola looked at the boys suggestively, her eyes glinting in the light of the street lamps. - 'Probably some old rats, sand, rubbish, nothing interesting,' Tymon shrugged his shoulders, but it was clear he couldn't hide his curiosity. - Or something that no one knows about yet - added Kuba quietly, as if he was afraid that someone would overhear. An hour later, they were already standing in a dark alley behind the bookshop, clutching torches in their hands and a bunch of keys that Ola had 'borrowed' from her grandmother. Her grandmother was the owner of the bookshop and more than once told her granddaughter about the old days when tunnels stretched under the market for merchants fleeing customs inspections. The door to the cellar squeaked ominously as they opened it. Dust, the smell of old books and something else, intangible, filled the air. A staircase led down, and around the corner, under a pile of decayed cardboard boxes, they found a walled passage. To their surprise, a good portion of the bricks were already out - someone had tried to get in. - Look! - whispered Ola, pointing to a shabby wall where an engraved sign was barely visible: three intertwined rings. They had never seen this symbol before. Tymon moved the bricks away and Kuba helped lever up a piece of the wall with a crowbar borrowed from a neighbour's shed. A passage was revealed, dark and narrow, leading into an unknown underground. The chill and the echoing drops of water heightened the tension. Ola was the first to slip inside, illuminating walls covered with strange, almost faded paintings. The tunnel led deeper and deeper, and their footsteps sounded deafeningly on the ground. Above their heads, somewhere far away, the sounds of the city rang out. Suddenly, around the next bend, Ola's light fell on something unexpected: a steel door with a combination lock and an inscription carved into the metal: "To the brave the world belongs". - Who would build something like that here? - whispered Kuba, touching the cool metal. - 'Maybe someone who didn't want it to get here easily,' replied Ola, looking around nervously. Tymon crouched down, looking at the castle. - 'Look, there are still these rings here! I think this is our key. They were just about to try their hand at opening the lock when a quiet, barely audible sound came from behind the door - as if someone was moving around in there. They held their breath. Was there someone else on the other side of the door?