Its where he grew up,the neighborhood that laughed at him cause his family was poor so he had to wear dresses, the place he had to safeguard against trolls and witches. Going back to that place of misery is ,i assume,very symbolic for doof.He did not break after all those years of in essence torture.
This is him just going back and admitting to himself that he made it big, that drusselstein did not break him,plus if his family still lives there,this maybe the moment he stands up to his father,gains their love and/or become a man through going down the highdive in the eyes of drusselstein.