World 8-Fortress is the fortress level, and the ninth level overall, of Dark Land in Super Mario Bros. 3. It becomes accessible after the player clears World 8-2 and its own completion opens World 8-. It is the longest and final fortress in the game.
Dark Land's fortress is made up of many doors and traps. The player starts next to some Roto-discs, above the third of which is a door that leads onto a conveyor belt over lava, which leads to a power-up with a Super Leaf. Continuing from the Roto-discs, the player will find a Brick Block containing a Fire Flower. The door above and to the right of the power-up will lead to a room with another Fire Flower, though the player has to first reveal Hidden Blocks to get to it while avoiding a Thwomp. Back in the first room, there is a door surrounded by Brick Blocks, and going through the door will put the player on a conveyor belt over lava. The next four doors lead to the same large room, though if the player finds the Switch Block in the Brick Block formation from earlier, there is a secret door that leads to a 1-Up Mushroom. The door under the Thwomp will also lead directly to a 1-Up Mushroom. Continuing over the lava, the player will come to a brick wall with a ? Block containing a Starman next to it. Dropping down through the gap and trying to jump out will reveal Hidden Blocks, with the right-most one containing a 1-Up Mushroom. Going through the door on the right, followed by the next door, will take the player to a conveyor belt with spikes above it; if the player is powered-up, they will have to crouch under them. Continuing up the stairs and moving to the far right, the player has to drop down while avoiding the sliding Thwomp underneath and move to the left. Hitting the block closest to the conveyor belt will produce a Switch Block, and pressing it will reveal a white door on a ledge to the far right, which leads to Boom Boom, who is fought on a conveyor belt. The Switch Block will also reveal a door on the conveyor belt, which leads to a Fire Flower. Defeating Boom Boom will clear the fortress and open the way forward on the map.