World 1-1 is the first level of World 1, and subsequently, of New Super Mario Bros..
The first level in New Super Mario Bros., is a meadow with flowers, bushes, and mushrooms scattering the land. Princess Peach's Castle is visible in the background for the first portion of the level. The level introduces the Goombas and Koopa Troopas with both red and green shells. It also introduces the Mega Mushroom.
The first ? Blocks that Mario encounters have 2 Coins in them, and one that has a power-up. Going on into the level, Brick Blocks appear. The top one contains 14 coins and a Super Mushroom. Underneath that one contains 1 coin, while the rest are simple Brick Blocks. Mario then encounters a Goomba, who he stomps on, being next to a Pipe. The Pipe is not able to go down to, however. Mario encounters another Goomba shortly after. Then Mario then jumps over a pitwhile collecting coins. A block is struck about 1/3 through the level, and a Mega Mushroom is encountered for the first time, making Mario become the huge Mega Mario, destroying everything in its path. However, if the player chooses not to get the Mega Mushroom, they should keep advancing. The player will now see their first Star Coin. There are some Koopa-Troopas and a Goomba in this area. There is also a hidden vine that leads to the sky with Red Coins. It is located inside a Brick Block where the Red Koopa Troopa is walking. The pipe that's currently visible to the player leads to an underground room with a Star Coin in it, and a power-up. The player will see 3 Brick Blocks with coins in them, but if the player jumps on top of the middle Brick Block, a Star will come out of it. Another ? Block will be here, this time containing a power-up. A set of Brick Blocks will be blocking the second Star Coin; the player has to ground pound it to break it and get the Star Coin. Another ? Block will be here, containing a single coin. A couple of Goombas and Koopa Troopas will appear in this area, along with Brick Blocks and Coins. The player will now see the flag and finish the level. They will now gain access to World 1-2. There are a few vines leading to platforms and other things and an Invincibility Star is found above a Brick Block before the end of the level.