I really enjoyed this book. I thought it was a lot of fun too. It's always exciting to read a book that takes place in a location that you've been so that you can visualize it. The well and the donkeys is the main part of the tourist attraction of the castle. I asked a friend who grew up on the Isle of Wight if he read it as a boy. He said everyone knows of that book, but he has not read it.
A few weeks ago I watched the 2013 movie edition. I did not like the movie because it changed a big part of the plot. In the book it is important to John that he not succumb to the curse of the diamond and stays on course with his moral compass despite the hardships that he has to endure including imprisonment. It's why he can go back home at the end of the book and regain is life.