You need to complete the prologue to get to the Sky Castle, head forward across the bridge and enter the foxhole to your left.
To complete a Puzzle you must get the fox pieces to the green circle pads.
Piece 1 (Top left corner)
Piece 2 (Top right corner)
Use X to push each piece
Piece 1: Push it down and right to the bottom right corner.
Piece 2: Push it down, left, down, right and down.
Piece 1: Push it up and right.
Collect the page and the achievement will be completed!