This is one of the most popular books in French (and translated into many other languages)
It is highly recommended for French comprehension and vocabulary, as well as giving many insights into human nature ... beginning as a book for children and developing into a work of adult psychology ... with a mysterious ending. As you read chapters progressively it would be interesting to read your opinions in comments.
To read the entire book copy and past the link to view the book in PDF format.
The coloured drawings excellently illustrate the author's themes.