You come across a childs reading room as you make your way through the libary. It's quite obvious but if your not sure you will see a panda bear floating into a door which then shuts.
You have to enter through a door behind you, as soon as you enter press to use the PKE scanner. In the middle of the bookshelf's and in the middle of the room you will find a hop scotch games drawn on the floor. Leading away from the hop scotch you will find footprints leading to a tree with a dancing bear. Follow the hands prints around the wall which are behind the tree, this will lead you almost back to where you started.
Scan all the things you see in this video, hop scotch, handprints, bear. Once you do that the achievement will unlock.