World 2-3 is a sewer level in New Super Mario Bros..
It is mainly an underground level, although the first part is aboveground. At the very start of the level, Mario should go through the green Warp Pipe. The player should then press down on the D-Pad, making Mario slide through a tunnel and knock over Koopa Troopas. In the first actual room of the level, there are three Question Blocks, and in the next room there is the first Star Coin. Mario then must ground Pound through a manhole cover-like object to progress. He then comes across a door with an arrow on it that automatically opens when he touches it. In the next room, Mario will find a Question Block and a Swooper. If Mario ground pounds on the arrow door just past the Swooper, he can enter a room with a block that he can repeatedly hit for many coins. In order to proceed, Mario needs to pound on two more manhole covers. Once he has pounded through all of them, he can either proceed or jump up to another room with two blocks in it. If he chooses to jump up, he will have to pound through the covers again. When Mario goes into the next room, he will find a Super Piranha Plant.. Mario can either run straight through it and get hit, or he can avoid it by passing through the arrow doors. The second Star Coin is here, and there are two ways to get it. The first way is defeating the Super Piranha Plant, but this can only be done if Mario has the Fire Flower. The second way is to go to the right, jump, go to the left, jump, follow right, go down, and then fall on the small platform under the top platform to get it. After this, Mario will go into the next part of the level, which has some water in it. The Midway Point is also located here. In a nearby room, there is a normal ? Block and a secret block, which will wield a 1-Up Mushroom. Mario can press the ? Switch here, and it will make the water rise. There are two things Mario can do. The first is simply swim to the right, which is the main way. The second is swim up into the next room, where there are many coins. If Mario is quick enough, he can get the water to rise again, which will let him get to the secret exit, and allow him access to World 2-A. If Mario continues the normal way, he will find another Super Piranha Plant. There are several coins above this one. In the next room after that, there are two Question Blocks, one of which contains a power-up. Mario will then enter a large series of rooms, one of which houses the third Star Coin. The way to proceed is to go right. After Mario exits the sewer area, he will find a spring. Mario can jump on the spring to slide down the flagpole.
- Star Coin 1:Near the beginning, before you ground pound into the first manhole, there is a space above. Use this space to wall jump off the right wall and onto the left ledge. Once you're on the ledge, the Star Coin will be in the small room.
- Star Coin 2:Once you get into a room with multiple arrow doors and a lone Piranha Plant, there are a few ways to get this coin. However, the safest way is to kill the Piranha Plant and then wall jump up to the Star Coin.
- Star Coin 3:Once you get past the massive Piranha Plant and go up into the large room, go left towards a Piranha Plant. Once you get past that Piranha Plant, there will be two different chambers where you use orange platforms to get to the top. Go up the right chamber then once you're at the top, run across over the gap to reach a ledge on the other side. Once you're there, the Star Coin will be in the small room.