I think Page 95 of the pdf walkthrough has a map of that guild, if I'm not mistaken:
https://www.aldorlea.org/Laxius_Force_free_Guide.pdfBased on the instructions, I would assume you start at the guild, go through the bottom-right area that has two bare, frozen trees and follow the path all the way to the very top right of that image.
I think it's one of those end of chapter secrets that only appears after you've advanced the plot to the very end of the chapter, so you may need to go as far as defeating the enemy the walkthrough mentions using fury against; before the rabbit actually appears. But don't talk to Louis, or you can't turn back anymore.