Lena never expected that an ordinary Saturday could suddenly turn into something so unusual. She was sitting on a bench in the city park, hooking pebbles with a stick, when Bartek ran up to her with his hair dishevelled and his eyes shining with excitement. - Come on! - he called out, grabbing her by the sleeve. - You have to see this! Before Lena could ask what this was about, they were already running together through the park alleys until they reached an old, mighty oak tree. It was beneath it that they often drew with chalk on the pavement or built nests for sparrows out of the leaves. This time Bartek pointed to the ground behind the tree. Lena noticed something unusual: a small hollow had appeared among the roots of the oak that had never been here before. - Look, there's something there... - whispered Bartek and carefully slid his hand into the dark opening. Suddenly his hand disappeared, as if there was no earth there, only air. - Ouch! - he shouted and withdrew his hand, but nothing happened to him. His eyes shone even harder. - This is no ordinary hole. Touch it yourself! Lena, a little frightened but also curious, put her hand on the moss. Instead of roots, she felt something cool and smooth, as if she had slipped her hand into a stream - even though it was dry all around. They looked at each other communicatively. - Do you think this is... some kind of passage? - Lena asked, and Bartek nodded. Without thinking for long, they pushed their heads into the opening and suddenly felt as if everything was spinning. Colours blended together and sounds became stretched and strange. When they finally materialised on the other side, they were amazed to discover that the oak tree they had just been under looked completely different - its leaves were purple and silver lizards were climbing up the trunk. In front of them stretched a clearing where unfamiliar plants with glassy stems grew. Luminous orbs floated in the air, and figures flitted lazily in the distance: something between a cat and an owl, with long, downy tails and bulging eyes. Lena and Bartek looked after each other in awe and disbelief. - Where are we? - whispered Lena, clinging close to Bartek. Suddenly, someone or something emerged from behind a bush - a tall creature in a cloak of feathers, with a face that could not be fully seen. Its hand pointed at them, and its voice sounded strange, as if it was echoing: - You have arrived just in time.... Lena and Bartek froze, wondering what would happen next.