World 4-4 (Super Mario Bros. 3)
From the Super Mario Wiki
World 4-4 is the fourth main level and the fifth level overall of Giant Land in Super Mario Bros. 3. It is accessible once the player clears World 4- 1 and its own completion unlocks Worlds 4-5 and 4-6.
The player starts on a small platform over a body of water, and a Lakitu throwing Spiny Eggs will soon move into view. Directly below the player on the waterbed is a pipe that leads to a secret room with coins, though the player needs to enter the level wearing the Frog Suit in order to move past another pipe blowing bubbles, which push the player upward. Moving right from the starting area, the player can find the level's only ? Block containing a power-up, which will be either a Super Mushroom or Fire Flower depending on the player character's state. Sinking down a narrow passage afterward, the player will be brought to an open area with several large Wood Blocks where the player has to continue avoiding Lakitu's Spiny Eggs that are being tossed into the water. At the end of the area is a Warp Pipe leading to the goal.
The water level is evened-out in the Super Mario All-Stars and Game Boy Advance versions. In the original version, due to the differing water levels (higher at the beginning, and lower after the giant Wood Block wall), it was possible to access the secret area without a Frog Suit.