Carry this switch a little past the half way mark until you reach two pipes with red guys jumping out of them. Put down the "P" switch, step on it, and run back to the start of the level. While your running there will be a lot of silver coins on the way. Get all the silver coins you can and you will gain 50+ lives!

Important: Be sure not to kill the Koopa Troopers (or the green junping guys) on the way to the "P" swich, those guys turn into the coins that give you the lives.

After passing through the moving horizontal rocks and going through the yellow pipe, there is a long passageway consisting of a moving rock formation and a flying ‘?’ Block. (If you are equipped with a Yoshi, do not hit the block, because it contains a pair of wings, causing you to bypass the whole level.)

When you pass the moving corridor and go through the green pipe, there should be a yellow rock floor. (You must run past this before the rock crushes you.) Simply fly onto the brown ledge above said rock, and move left. A short drop will lead you to a key and keyhole.

Pick up the key, insert it in the keyhole, and you’ll be warped out of the level. This action will reveal a path to a Fortress on the map screen. Defeat the Reznor, and a path to Bowser’s Back Door.