The Wonderful Wizard of Oz, by L. Frank Baum, Penguin (originally published in 1900).
L. Frank Baum was the J.K. Rowling of his day; or, she is the L. Frank Baum of modern times.
They both weave amazing and intriguing tales that span several books, but each book is self-contained. And yet, neither excels especially at the craft of writing. Even so, the content SO outweighs the delivery that both writers are brilliant.
For those who have seen the film, the book is close, and also completely different. The land of Oz is FAR more intriguing in the books than it is in the movie.