Head right from the start, dodging through the obstacles of the Fortress until Mario arrives at an area with a Power-Up, a Dry Bones, and a door.

Warp Whistle Two The second Whistle is to be found in the World One Fortress. Keep running right to enter into a hidden Mushroom House to gain access to the Whistle from a giant Treasure Box! Keep in mind that if you are jumping around behind the black scenery, you may jump the entrance to the Mushroom House, so just run along the ground). Now Mario has the ability to walk behind the scenery (including other blocks and bushes), so run to the right at top speed to get behind the black at the end of the level (this will be the same area as the Card Box). Get onto the White Platform (the only one in the level), duck down (hold DOWN), and after 5 seconds Mario will fall through the block. To gain access to it's hiding place Mario must go towards the end of the level to the point just short of a Para-Goomba that drops Micro-Goombas. Warp Whistle One The first Whistle to be found is located in World 1-3.

Super mario bros 3 world map module