World 1-Tower is the fourth level and the tower of World 1, and subsequently, the first tower of New Super Mario Bros. The boss here is Bowser Jr.
The player starts out on a rising and lowering platform if which the player stays on it for long enough it will go down and this will reveal four coins. Mario then progresses encountering the first Dry Bones of the tower and the game. The player then keeps on going up finding two ? Blocks, one containing a coin and the other either a Super Mushroom or a Fire Flower depending on what form Mario is. The player continues to progress up the tower but some platforms appear pushing out from the walls. If the player gets squashed in between the platforms the player will lose a life. On the last platform he encounters another Dry Bones. Still going up, the player has to jump up a couple of platforms, then the player has to turn right encountering platforms trying to push down on Mario. The player continues to progress up finding finding another group of platforms. The player finally reaches to the last one which Mario is on top of the platforms, here the player also encounters another Dry Bones. The player will also find a Star Coin and two blocks, one is a brick block block and the other a ? block. The normal block contains coins while in the other block there is a Mushroom or a Fire Flower. The player progresses up finding platforms pushing out of the wall which if the player can pass them fast enough they will appear as a stair case. The player has to go up it finding the player in between an unusable door and a Warp Pipe. The player can go into the warp pipe which will shoot the player, making Mario reach the check point.
The player either go up towards the Door or go down to get more coins. If the player decides to go up, the player finds a warp pipe cannon that will blast Mario past a series of moving platforms. If the player times it right Mario will get to the boss door easily, if not the player will lose a life by being crushed between the platforms. Here there are two Big Dry Bones trapped in two enclosed platforms. The player also finds a ? Block which contains either a Mushroom or Fire Flower. The player has to enter the door in order to progress. The player will now find Bowser Jr., who challenges Mario to a battle. Bowser Jr. will run around the room, trying to run into Mario.
After his first defeat, Bowser Jr. will then take Peach away with him to the castle of World 1.