Forest Fortress is a secret Fortress found in Super Mario World. It can be accessed by completing the level Forest Secret Area in the Forest of Illusion. By completing this level, the player gains access to Star Road, located in front of Star World 5. Although officially part of the Forest of Illusion, it is situated out of the forest on the overworld map.
Mario will start out in a moving sidescrolling area. He will find Pillars throughout the area. After getting past the first Pillar, Mario will also find Grinders moving along dotted lines close to the ground. The player may have to use the Spin Jump to get past the obstacles. After progressing through the area, Mario will even find bottomless pits under the Grinders; however, these bottomless pits will be completely covered by Exclamation Mark Blocks if Mario has activated them before the level. At the end of this area, Mario will find a door taking him to the next area in the fortress.
In the next area, Mario will start out on a platform above the lava. A Grinder will immediately fall from a big rectangle platform at the top of the screen. Mario must jump over a pit full of lava, avoiding the Podoboos that jump out. After climbing the next platform, Mario must jump into a small pit at the bottom of the screen, which contains two Grinders and a Triangular Block that Mario must use to climb out of the pit and progress through the level. Mario will find a Question Block on the platform containing a power-up. Next, Mario must get a running start and jump across a pit of lava (with Podoboos in it). The next platform is a long area made of a set of unbreakable gray blocks (and Podoboos and Grinders). Mario can either stay on the flat platform or jump across the blocks suspended above the ground, avoiding the Grinders and Podoboos. When Mario reaches the end of the platform and jumps across the lava again, he will land on the last platform of the fortress. If Mario is on the part of the platform at the bottom of the screen, he will find a Triangular Block that will help him climb the wall and reach the boss door. Mario must, again, fight four Reznors on a set of four rotating platforms by hitting the underside of each platform.
This exit can only be accessed with Cape Mario. At the last platform in the fortress, Mario must stay on the part at the top of the screen. This way, he will be able to jump onto the row of blocks above the first boss door. When Mario reaches the wide pit of lava, Mario must jump while dashing, activating Cape Mario's gliding ability. If Mario flies far enough without getting hit by a Podoboo, he will reach a secret platform. This platform contains many Rotating Blocks with 1-Up Mushrooms, and the second boss door. In the boss door, Mario has to fight four Reznors again, in the same manner as the normal exit. After completing either exit, Mario will be able to access the Star Road and go to Star World 4.
The alternate exit does not count as a secret exit. As a result, the player is not required to take it to 100% complete the game.