As you can see, the base of the book is made from 4 matchboxes which is where the secrets comes into play.
When I think Da Vinci I also think steampunk so that the way I went with the decoration.
Small tags with Da Vinci drawings and stamped images
Pocket page with tags
Extended page with fold flap
Stamping and embossing
Embossed stamping and downloaded da vinci drawings.
More embossed images
I used lots of downloaded da vinci drawings and paintings
I attached the pages to the spine so that it will open and lie flat so that you can get to the fourth drawer that is on the spine of the book.
This shows the drawers open with lots of bits and bobs inside.