Behind the Walls is a little blue book that appears in the Disney Junior animated series, Sofia the First. Hidden inside the book, A History of Enchancia Castle, this book is also the key to the Secret Library.
History
During the reign of King Roland I, his daughter Matilda came across or was given a book called A History of Enchancia Castle. Inside the book, she found the book known as Behind the Walls when she reached Chapter Seventeen. Suddenly, the Amulet of Avalor, which she was wearing at the time, glowed blue and led her through a secret passage way to the Secret Library where Tilly became the Storykeeper. Third years later, she gave all that to her niece Princess Sofia.