This is the second secret level in the world.

It has a red-flag exit which unlocks a different path that leads to World 3-B. This is the second level in the world, and mostly takes place on tilting mushrooms. This level is the first secret level in World 3. Cheep-Chomps appear here for the first time in the series and make their only appearance in this game. The first level in World 3 takes place underwater.

World 3 can be skipped if the player gains access to World 4 by defeating Mummipokey, the boss of World 2, in mini form. After the completion of this world, the player instantly gains access to World 5.

World 3 has a total of eleven exits, and the boss of the world is the Cheepskipper. This world features a large beach-covered island, with many ocean- and beach-themed levels featuring Cheep-Cheeps, as well as the first Ghost House in the game. World 3 is third main world in the game New Super Mario Bros. But don't expect to be lounging on the beach - this world is far from paradise!” - Official website “If you don't find the alternate exit in World 2, you'll find yourself in the tropical landscape of World 3.

World map super mario bros 3.