Big Montgomery's Fort is the fourth level of World 1 in Yoshi's Woolly World it is a fortress that features lava and see-saw platforms, and contains the first mini-boss Big Montgomery.
The level starts out by an egg block, before a section with some ball and chains. Partway through this section is a platform that needs filing out, and this platform will allow the player to collect some beads, and if they jump right, they can get a piece of Wonder Wool and a Smiley Flower. The player then goes through a door to the next area.
The next room has a checkpoint and some platforms made of wool, before leading to area with Lava Drops, and see-saw platforms that need to be used to progress up the room. At the top of the room, the player will have to go across some more wool platforms, whilst avoiding some ball and chains. At the end of the room is another checkpoint and a door.
The next room has Monty Moles that jump out of walls and ball and chains, at the end of this room, the player will need to eat part of the floor to reveal the Boss Door.