There are three normal Warp Whistles in Super Mario Bros. 3. Two are in Grass Land and the third is behind Desert Land’s northeastern rock. Each whistle is a consumable map item; keep them unused if you want to play every world in order.
World 1-3 — behind the scenery
Stand on the white platform near the goal and hold Down for about five seconds. After Mario drops behind the scenery, run right behind the black goal backdrop. Enter the hidden house and open its single chest. The effect is temporary, so move directly to the goal area. Open the world walkthrough.
World 1 Fortress — above the ceiling
Keep or collect a Super Leaf before the first visible door. Run to fill the P-Meter, fly above the ceiling and continue right to the hidden doorway. Press Up and open the chest. A Mushroom alone cannot provide the required flight. This finish leaves the fortress’s map lock closed. Open the world walkthrough.
World 2 — behind the northeastern rock
Defeat the wandering Boomerang Bro whose reward is the Hammer. Use that map item on the far northeastern rock, then enter the hidden passage. The nearby Toad House supplies a Frog Suit. Defeat the pair of Fire Bros. beyond it and open their reward chest for the third whistle. Open the world walkthrough.
Choose a warp destination
Use a whistle on the map to enter the Warp Zone. From World 1, it offers Worlds 2, 3 and 4. From Worlds 2–6, it offers Worlds 5, 6 and 7. Using a whistle in World 7, World 8 or the Warp Zone itself leads to World 8.
For the familiar two-whistle shortcut, collect the two Grass Land whistles, use one on the map and use the second while still in the Warp Zone. This skips directly to Dark Land. Skipping a world does not count as completing all of its courses.