The Deep Learning book is great & I have a copy, but its not honestly something that I read cover to cover.

To me, Its more of a reference book.

But if you want a "Fyneman" type book that describes the underlying structure & workings in a non academic way, I would recommend;

Michael Nielsen's Neural Networks & Deep Learning[0]

Jeff Heaton's Introduction To The Math Of Neural Networks[1]

[0]:http://neuralnetworksanddeeplearning.com/index.html

[1]:https://www.amazon.com/Introduction-Math-Neural-Networks-Hea...