Classic NES Series: Super Mario Bros. Cheats

Go to world 1-2.
At the end of the level, there is a pipe, and some bricks.
You must smash the second to last brick and the third to last brick as seen to the left.
Now you must stand on the edge of the pipe, duck, and face left
Now jump to the right towards the one block that you didn't break, while facing left
You should slide right through the bricks, go into the first pipe when you get to the other side.

You should be warped to the minus world, the level is -1.