Castle Key

The Castle Key is an item found in Bowser's Castle in Paper Mario, during Chapter 8. Upon reaching Bowser's Castle, Mario discovers the front door is locked. After going right, he discovers a side entrance. Once inside, after defeating a Koopatrol, Mario will obtain the valuable Key to unlock the front door and continue his quest.

In Paper Mario: The Thousand-Year Door, there are four Castle Keys in Hooktail Castle. The first one is on a ledge near the flippable switches, and it opens the door to the right. The second is behind the cells on the first floor. Mario and co goes back after getting the Paper curse to get it to access the second floor. The third is in the storage room on the third floor, where Mario encountered Ms. Mowz. It opens the door to the right. The fourth is in the right of the third floor. It opens the first door on the fourth floor, to the outside.