World 3-Fortress is a fortress level in New Super Mario Bros..
When Mario spawns in, there will be three green pipes. If you go in the middle one, it can launch you up to one of the chain walls to progress. However, if you wait till you can climb on the lowest chain wall, move to the left and climb up the chain with the 3 Climbing Koopas. Go in the room above and the first Star Coin will be in there. After that, go back down to the pipe and climb up until you get to the 4 Amps that are blocking the way. You will have to punch the middle part of the chain wall to swing around to the other side, then jump up to the next area. Now, jump up to the chain wall with the lone red Climbing Koopa and break the 2 brick blocks above to get to the next area with more brick blocks above to break. Once those blocks are broken, jump up to the chain wall with four more Amps to swing back around to the front side of the chain wall. Then, you will have to ground pound through the brick blocks in the bottom left, and the second Star Coin will be on the chain wall next to you. Once you have that Star Coin, go back to the chain wall that you used to get on the front side, and you will notice two brick blocks in the top right. Break those and go through the door in the little room above. Inside the room will be a red switch off to the left. Once you press it, you will have to quickly make your way to top, switching between chain walls and red platforms before the timer runs out. When you're at the top, the last Star Coin and the door to the next room will be there. In the room will be a chain wall with 2 Question Blocks above and 3 Climbing Koopas. Jump off the chain wall down to the door leading to the boss fight, which is Bowser Jr. Nothing really changes in this fight, except that there is water under the area. Every time you hit Bowser Jr. though, he speeds up. After two hits, he will also start jumping. Once you defeat him, Bowser Jr. will take Princess Peach to the World 3-Castle and the level is completed.
- Star Coin 1: Use the cannon pipe to get on the low-most chain wall, then use that chain wall to jump up to the chain wall with the 3 Climbing Koopas. Then, go in the room above this chain wall and the Star Coin will be in there.
- Star Coin 2: Once you are back on the front side of the chain wall, ground pound through the brick blocks below and the Star Coin will be next to you on another chain wall.
- Star Coin 3: Once you have the second Star Coin, go back to the chain wall with the Amps and in the top right you will see some Brick Blocks. Once you break them, there will be a door in a small room. Go in the door and you will find a red switch. When you press it, you will have to quickly make your way to the top, switching between chain walls and red platforms before the timer runs out. At the top will be the Star Coin and the door to the next room.