Gilda, a cow on Mean Street, will offer you a quest to retrieve an axe from the Slopes area of Mickeyjunk Mountain. Get the axe and head to Oswald's lair. Thin Oswald's massive face in the floor to find a hidden room. At the end of the secret passage you'll come to unthinnable bars. DO NOT use the axe to explore the area. Instead, go back to Gilda. You can return to Mickeyjunk Mt. later in the game and pry open the bars anyway -- even without the axe. For this you will get both Hero and Scrapper credit.