A Clue to the Secret Book

I heard in is going through hard times... I should go check on him.

At the VIP sauna in , I met this bald man called . He has a son, and apparently he ran away from home one day with a book that he cares deeply for. He requested that I find his son and get the book back from him. For a reward, he's offering me a nice sauna robe. He also told me his son hangs out at a tree tunnel around , so maybe I can find him there. Anyway, is that book more important to him than his son?? What kind of a book is it anyway...????

I found in the tree tunnel of , as requested by , whom I met at the .