World 5-Ghost House (New Super Mario Bros. Wii)
From the Super Mario Wiki, the Mario encyclopedia
Common Ghost House enemies can be found, including Boos. More of a maze than a typical ghost house, this house has a multitude of doors in each room; with some paths instead leading to dead ends. Since most of the doors are either fake or go in circles, there is only one successful path. To add to the difficulty, it is a very dark level.
To get to the path that leads to the exit, Mario and co. must fall into the first gap, jump across the second and third gaps, fall into the fourth gap, and jump across the fifth gap.
To get to the secret exit, Mario and co. must fall into the first gap, jump across the second and third gaps, and finally, fall into the fourth and fifth gaps, where they must go through a hidden passage to the left-most door. After making it past the room, they will reach the secret exit, with only a lone Boo and a group of Circling Boo Buddies standing in their way.