World 2-3 (New Super Mario Bros.)

World 2-3 is the third level of World 2 in New Super Mario Bros., and the only sewer level in the game.

Layout
The level begins in a desert with a Warp Pipe. When Mario enters through the pipe, he enters the sewers, and slides into several Koopa Troopas before reaching the bottom. On some platforms, Mario will have to Ground Pound in order to pass through them. Flippers also appear, and will open when Mario collides with them in the direction the arrow on them is facing. After Mario crosses a Flipper at the bottom near the beginning will lead the player to a Coin Block. After ground pounding and crossing the area, Mario will have to solve a small puzzle to collect the first Star Coins, located above a Piranha Plant, and also to go to the next part of the level.

After crossing the puzzle, Mario will cross the midway point and then he will have to slide in order to proceed. In the left corner, he can find a ? Block with a coin inside, and to the left of the block is a Hidden Block containing a 1-Up Mushroom inside it. The player will not be able to reach the big platform to the right, because they need to press a ? Switch first. Pressing the switch will cause the water level go up in order to reach the platform, or the secret exit that is located at the top. If the player goes to the level's normal exit, the player will find a Super Piranha Plant. After passing the Super Piranha Plant the player can go to the right path, where Mario can find two ? Blocks, one with a coin inside and the other with a power-up inside. The top path of the level contains a puzzle, where the third Star Coin can be found to the left. Mario can find the normal exit to the right, but before he can reach it, Mario should press a ! Switch to active some blocks in order to reach the exit. The player can use the Trampoline at the end of the level to get a 1-Up Mushroom at the top of the flagpole.

Secret exit
When the player hits the ? Switch, they will need to swim upwards into another room filled with Coins and Dash Coins. They will need to hit another switch, which will raise the water level once more, which will last for only a short period of time, as the water level will go back down once it reaches the top. Taking the exit to the right will lead Mario to the secret exit and access to World 2-A.

Star Coins

 * Star Coin 1 - The first Star Coin is located in the very beginning of the sewers, towards the right. The player will have to Wall Jump to reach the platform where it is located.
 * Star Coin 2 - The second Star Coin can be accessed by the player in two different ways. The first way is to defeat the Super Piranha Plant, which can only be done if Mario is in his Fire Mario form. The second way to do it 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.
 * Star Coin 3 - The last Star Coin can be found in the level's last maze, where the player has go to the left side and after jumping of a small brick bridge, the player has to follow the right path in order to get it.

Trivia

 * World 6-3 from New Super Mario Bros. Wii is very similar to this level.
 * Trying to jump upward through the small gap between the two downward-facing Flippers near the end of the level will get the player stuck briefly.

Mondo 2-3 (New Super Mario Bros.)