Grotto Key

The Grotto Key is a key found in Pirate's Grotto in Paper Mario: The Thousand-Year Door. It can be found in the storeroom in the left of the north area. After encountering an area with vertical stairs to the north, Mario realizes that the door in front of him is locked. Frustrated, Mario takes the stairs to the north and go left. Eventually he encountered a storeroom with this key. (Ms. Mowz doesn't appear here.) To retrieve it, Mario must use Kooper or Admiral Bobbery to activate a switch in the storeroom while he heads for the wooden lift. After taking the wooden lift, Mario easily grabs the key on top of the barrels to the right of him.

The key opens the door on the right of the big stair room. The next room is a dark one with three Parabuzzies.