World 6-Fortress 3

 is the third fortress level and the thirteenth level overall of Ice Land in Super Mario Bros. 3.

Layout
The fortress has many conveyor belts and Roto-discs, many of which are positioned over spikes. There are also a couple of Boos in the fortress as well. High above the gap between the second Roto-disc and conveyor belt is a block containing a 1-Up Mushroom, which the player can reach if they start the level with a flying power-up and use the straightaway at the start to build the Power Meter. After the second conveyor belt is a ? Block with a power-up placed between two Stretches, with another power-up placed over the third Stretch ahead. The next conveyor belt has a Thwomp above it, and some Coin Blocks on the platform above the player can reach by flying. After the conveyor belts is a Duo-Roto-Disc placed between two Stretches and over a pit of spikes. After the final jump, there is a door that will drop the player into a room with three Boos. The room's floor will rise, allowing the player to reach a door on the right. Through the door is Boom Boom, in a room with five blocks he will jump between.

Enemies

 * Roto-discs
 * Boos
 * Stretches
 * Thwomp

Level statistics

 * Power-ups: 2 (Super Mushrooms or Super Leaves)
 * 1-Up Mushrooms: 1
 * Secret areas: 0