The House Key is an item in Paper Mario: The Thousand-Year Door that is needed to be found for Mario to complete one of the troubles from the Trouble Center. The House Key belongs to Garf who has lost his key and isn't able to get inside of his house. When Mario finds the key and returns it to Garf, he will receive twenty coins. The Key is near Zess T.'s roof.
 Trouble Details
Garf: Find my key!
They call me Garf. I have lost my key and, thus, cannot get into my house. It should be somewhere in Rogueport. I just need someone to find it! I'll be waiting for you at the house at the very back end of east Rogueport.