Find and use the six hidden buttons in level B of this chapter. To find 
the first button, when you first start destroy the black object in the 
wall in front of you. After you pass under a large gun and you will walk 
into an open area with three more black objects. Destroy the black object 
in the corner opposite the entrance to the area to find the second button. 
Then, go up the small ramp and wait until two bridges appear, on one side 
of another large gun. Use a charged jump from the bridge to reach a platform 
above the large gun to access a hidden room with the third button. Proceed 
through the level until reaching an area with three doors that enemies are 
appearing from. There should be two small doors to the right and a large 
door under a turret farther back (which leads to a tunnel that contains the 
fourth button). To find the fifth and sixth button, get to where you must 
use a switch to create a bridge. Do so and start crossing it. 
While walking across the bridge, look to the right to find an alcove with 
two large explosive objects in it. Destroy both of them to find the last 
two buttons. Note: Use the button closer to the start of the bridge first 
or the secret pipe will remain locked. After all six buttons are used in 
order, the locked door at the end of the bridge can be opened, leading to 
the secret Super Mario Brothers pipeline.