New Super Mario Bros./World 2-3

Dive into the elaborate sewer system where the Piranha Plants call home. Don't get lost within this large labyrinth of pipes and chambers. Flippers and covers either impede or assist you in your journey. Why is there a sewer in the desert? Perhaps it's a hint that there's water nearby...

Level walkthrough
To enter the main level, you must first enter the warp pipe at the start of the stage. You will defeat several Koopas as you enter the sewer, then get dropped off into a large chamber. Go right until you reach a vertical shaft with a manhole cover preventing you from dropping in. Here, wall jump up the shaft to reach another room with the first Star Coin. Drop back down to where the manhole cover is. You must ground pound the cover to fall through it. In the following chamber, there is a lone block containing a power-up as well as a single Swooper. There is also a one-way flipper that you can fall into, which takes you into a small room with a 10-coin block. You'll have to climb back out using the shaft to the right. To progress, jump over the flipper and up to the shaft at the very left. Ground pound and keep holding down to smash through every one of the covers in your path.

Go right until you reach another chamber. There is a single Piranha Plant here as well as a bunch of one-way flippers. If you lack a Fire Flower or a Blue Shell, you will have no way to defeat the plant, so you must find a path around it. After going through the first flipper that takes you into the chamber, jump up and to the left. Go left and jump up to the next level, then move to the other side of the room, passing a Star Coin on your way. Drop back to the previous tier of platforms and go left to make last flipper form a platform above the second Star Coin, letting you collect it with ease. Jump back up to the top level and go right again, this time falling all the way down to the lower corridor. Go right to enter the next section of this vast level.

You will activate the midway checkpoint upon your entrance into this section. Slide down the slope up ahead until you reach a split path. Go left first and wall jump up to reach an irregularly shaped chamber. There's a coin block here, but you can also hit a hidden 1-Up block at the left side of the room. Return to the split path and go down this time. Walk right to enter a huge room with no immediate way forward. The next corridor is high up near the ceiling, too far for your jumps to reach. You need to jump up the small shaft at the left side of the room to reach a switch, which will flood the room, letting you swim to the exit. Go right to enter the final sector of this confusing maze.

You will encounter a Super Piranha Plant in the first chamber of this new section. It can be defeated the same way as any other Piranha Plant, but takes up more space. If you don't have fireballs or shells, just ignore the beast and jump over it. Go all the way right down the hallway to reach a small room with a power-up and a coin block. Go back left and go up once you reach a split path. Once up the slope, you will reach the largest chamber of the sewer system, with a ton of pathways that lead to different chambers containing various items. Go left and jump up the shaft past the Piranha Plant. Take the right path when the shaft splits, and keep jumping up. Go right and leap to the right to land on a thin platform next to the final Star Coin. Fall down and run all the way right this time. Jump up the shaft past the cover. You can go left for a power-up if you wish, but proceed to the right if you want to reach the exit. Jump up to the thin platform to reach a red switch. Press the switch to make some red blocks appear, which is necessary for getting to the exit past the Piranha Plant. Fall down and quickly go left, up and right to move on to the red blocks, then keep going to get to the exit to the sewers. Back on the surface, use the spring to jump straight up at the edge of the pipe to hit a hidden block. Jump to that hidden block and jump from there to help you reach the top of the flagpole.

Star Coins

 * 1) Near the beginning of the stage. Wall jump upward when you reach the first split path and you will get to the chamber that contains it.
 * 2) In the section with many flippers. Maneuver around the flippers to get to the coin.
 * 3) In the large room of the final section, go left and up the shaft, taking the right path when you come to a split path. Make a leap to the right to reach the coin.

Alternate exit
Back at the room that can be flooded, there is an opening in the ceiling. When the room is flooded, you can swim into the opening to reach another chamber with a bunch of coins you can collect. However, if you swim up fast enough, you can also see another switch, this time hanging from the ceiling. The switch is only visible when the first switch is still active, and pressing it will flood the room even further. This will let you swim up more to reach a hallway at the top. Exit the hallway to reach the red flagpole. This alternate exit opens a path to World 2-A, which itself leads to some major shortcuts.