The House Key is a key item that appears in Paper Mario: The Thousand-Year Door.
The House Key is an orange key.
The House Key only appears if Mario takes on Garf's "Need a key" trouble at the Trouble Center. The House Key can be found just outside Lovely Howz of Badges in the main area of Rogueport. The House Key will then permanently unlock Garf's house which is the easternmost house of Rogueport.