When Lena, Max and Oskar slipped out of the house on the last Friday evening in June, none of their parents could have expected what an extraordinary adventure awaited their children. The June nights were long and warm, and the air smelled of ripening grain and dampness after yesterday's rain. They trudged through old, overgrown plots on the outskirts of town, laughing and telling each other strange stories. Oskar, the oldest and most curious of the three, led them through the dark forest, holding a torch. He was the one who insisted on checking if there really was an old bunker - concrete ruins from the war, about which various rumours circulated among the youngsters of their school. Lena, fascinated by architecture and puzzles, eagerly searched for signs of the old entrance. Max, on the other hand, who usually preferred to spend his evenings with his guitar, this time gave in to the mood of adventure. Finally, when it seemed that their search would end in failure, Lena found a piece of cool, smooth wall under the lush ivy. Oskar immediately rushed to help him, and together they pushed back the vegetation. To the eyes of all three, a rusty door with a metal wheel in the middle appeared. - Really? It can't be that easy,' muttered Max, laughing a little nervously under his breath. Oskar pushed the wheel with all his might. Surprisingly, the door gave way with a groan. The inside of the bunker was dark and smelled of dampness and the dust of long unvisited places. Lena pulled out her phone, illuminating the space with a cool light. Silence reigned inside. Rust-covered metal boxes stood in places, and abandoned gas masks lay against the walls. After a few minutes of wandering around the stairs and corridors, they came across something strange: at the end of one of the tunnels, in a circular chamber, was a huge steel ring, laced with a tangle of cables and old electrodes, the ends of which glinted in the light of the phones. The ring looked like a fragment of some device whose purpose they could not guess. On the wall, right next to it, was a board with strange, glowing inscriptions in a foreign language. Lena touched one of the electrodes. At the same moment, the metal ring flashed with a pale blue glow and the air in the chamber trembled. - Oi... something feels like this is no ordinary monument,' whispered Max, taking half a step backwards. Before they had time to move, a streak of light shot out from the centre of the ring and began to spin, forming something like a spinning portal. For a moment, they could see beyond it a landscape very different from their own: mountains resembling purple crystals, floating islands and huge black silhouettes of beings whose shapes they could not see exactly. - Are we going in? - Oskar asked, his voice trembling but his eyes shining with excitement. They didn't know if what they were seeing was real or just the result of hazy light and their own imagination. Lena felt her heart beating faster and her hand squeezing the phone so hard that her fingers turned white. All three stood at the edge of the light, looking at each other and at the portal that seemed to pulsate, drawing them into the unknown. One step - and nothing would be the same again. Oskar made the first move...