World 3-Tower (New Super Mario Bros. 2)

World 3-Fortress is an autoscrolling underwater fortress level in World 3 of New Super Mario Bros. 2. It is the only level in the entire game to feature Spike Pillars. This level can be unlocked by completing either World 3-3 or World 3-A. This level has two exits - the first one unlocks World 3-4 and the second one unlocks World 3-Cannon and a green Toad House. Mario has 500 seconds to complete the level.

Layout
Mario begins on a blue platform above the water with a single Fishbone. A ? Block containing a Fire Flower can first be found, followed by a Warp Pipe in the water leading to the next area, which will begin autoscrolling upwards as soon as Mario enters the area. Two Fishbones can first be found, followed by moving walls, which will move after a set period of time. Some of these walls are spiked. More Fishbones will then appear. After all the moving walls, there are spiked pillars coming from the left and right. In between these is a safe zone where the checkpoint and a ? Block containing a Fire Flower is. After that, a Red Ring will then appear. More Fishbones and spiked pillars will then appear, followed by a green pipe. Warping through will lead Mario to a small area with a ? Block containing a Fire Flower and the boss door. Here the player needs to defeat four Reznors on a single wheel with four rectangular ? Blocks to clear the level.

Star Coins

 * Star Coin 1: At the beginning of the level, there is a hole on the left side wall in the water. Mario needs to swim into the hole and being careful not to swim too low, swim to the left to find the Star Coin above two ? Blocks above the water with a Fishbone.
 * Star Coin 2: In the second room, the player will navigate through several moving walls. The Star Coin is located above the second spiked wall on the right, guarded by two Fishbones.
 * Star Coin 3: After the checkpoint, there is a Red Ring which has 4 pipes in between. One of them is green, which is of different colours of the rest of the pipes. Entering it will take Mario to another area with the Star Coin. The player has to avoid the strong water currents to reach it.

Secret Exit
Mini Mario is required to access this secret exit. Just before the checkpoint and the area with the spiked pillars, there are two small blocks which will move away to make way for Mario to pass through. Following the block on the right will bring Mario to a mini Warp Pipe. Following the path will lead Mario to the flagpole.

This exit unlocks a green Toad House and World 3-Cannon.