The underground in their city was old, grey and a bit creepy. Zuza, Michal and Lena always passed by the closed, rusty entrance to the disused tunnel, but never had the courage to explore it - until that evening. Instead of going straight home after school, they decided to get closer. At first there was nothing there but cobwebs, rubbish and the quiet echo of their footsteps. Suddenly Michael noticed that one of the brick walls at the end of the tunnel was pulsating strangely with a pale blue light. Lena felt shivers down her spine. Zuza carefully touched the shimmering wall - and then it shifted under her fingers like a sheet of water. - Can you see it? - she whispered. The boy and girl looked at each other nervously, but curiosity won out. They took a step forward - and suddenly fell into the middle of a tunnel of light. A moment later they found themselves in a place that absolutely did not resemble an abandoned underground. Around them stretched a forest full of twisted trees with silvery leaves, and small, glowing creatures floated in the air. - Where are we? - Lena asked, trying to catch her breath. Far away, among the trees, the huge silhouette of something that resembled both an owl and a cat flashed by. The animal slowly began to approach them, with unknown worlds reflected in its eyes.... The three friends stepped back instinctively, but after a moment they felt a quiet rustling behind them. In complete silence, someone or something appeared just behind them - and then the sky was torn apart by a loud bang....