The Vanilla Fortress is a fortress, located on top of the Vanilla Dome in Super Mario World. It can be accessed through completing the level Vanilla Secret 3. This is the only underwater fortress in the game. Like the other fortresses, Reznor is the boss of this fortress.
The level starts off with the Mario entering a pipe to an underwater fortress. He must swim, avoiding Fishbones and Ball 'n' Chains. If Mario is in his normal form, he can go under the gap to a pipe that is a shortcut which leads to the next part of the fortress. However, if he isn't, he must either continue swimming to the right, or to become his regular size so that he can fit through the section. There will be a small section with Spikes with some Fishbones as well. After, a ? block with a power-up inside it can be found, and a bigger section with Spikes, Falling Spikes, Fishbones, Bony Beetles, and Dry Bones. A purple pipe should be on the ground. The player must enter it. The player can go through two routes, the top route, which has coins and Ball 'n' Chains, or the bottom one, which have Fishbones, Dry Bones, Bony Beetles, Ball 'n' Chains, and Thwomps. After, the player will come across two Ball 'n' Chains, and a lot of Fishbones. Mario should now come across a Yellow ! Block, a Dry Bones, a Bony Beetle, and a door. The player should enter the door to fight the four Reznors. Once they've been defeated, the player can now go to Butter Bridge 1.