Ada and Franek really enjoyed visiting the old library at the market square. Mrs Zosia, the librarian, always had interesting books for them and told funny riddles. One rainy afternoon the children were running between the bookcases, looking for a book about dragons. Suddenly, Ada noticed something strange. Behind the tall bookcase of fairy tales was a small wooden door, which they had never seen before. - Franek, look! - whispered Ada, pointing at the door. It was very narrow and had an old gold key in the lock. - Do you think we can go in there? - asked Franek with sparks in his eyes. The children looked over to see if Mrs Zosia could see them, and slowly turned the key. The door creaked and slowly opened. It was dark behind them, but something bright shone in the depths, as if a thousand stars were dancing on the ceiling. - Let's go! - whispered Ada. Franek grabbed her hand and together they went inside.... Suddenly they heard quiet voices and felt the floor begin to shake. What was on the other side of the door?