World 3-Fortress 1

 1 is the first fortress and fourth overall level of Water Land in the game Super Mario Bros. 3. This level is accessible upon completion of World 3-3, and its own completion unlocks World 3-4 and World 3-5.

Layout
This level begins with Mario running into a Roto-disc spinning clockwise over a Dry Bones. Mario then comes across a stack of gray blocks and another Roto-disc to the right of these blocks. After this Roto-disc is avoided, Mario encounters a series of gray blocks in the shape of a small staircase. At the drop-off of these blocks is a gray, unaccessible Warp Pipe. Mario then encounters the level's first Thwomp and three Warp Doors. These Warp Doors will lead Mario to three doors that drop him off in a body of water, presumably the basement of the fortress. Three Cheep-Cheeps swim in this water and there are a total of three gray Warp Pipes. All of these Warp Pipes lead to the first pipe that Mario encounters, right before the first Thwomp of the level. There are two ? Blocks in the water area: one to the right of the first Warp Pipe and one between the second and third pipes. These blocks produce a Super Mushroom or Super Leaf, depending on Mario's current status. Back in the main area, a Boo resides next to the third Warp Door. Another Thwomp separates Mario from the next set of three doors and another Boo that is located next to the first door of its respective series and fourth overall. This door leads Mario to a platform that sits above the water in the fortress's basement. There is a ? Block on this platform which holds a 1-Up Mushroom. The sixth total door and third of this set of doors leads to a door above the water in the basement of the fortress. This door leads Mario to a platform of gray blocks, leading him up to another door which leads to Boom Boom. A third and final Thwomp separates Mario from the next set of three doors. More Dry Bones are seen here, too. The ninth and final door leads Mario to a room with fourteen coins encompassed within gray blocks. These coins are accessible from the top, and can be gathered by hitting the two Hidden Blocks above the door. The Boom Boom of this fortress grows wings after the first hit, and flies around the room until defeated.

Enemies

 * Roto-discs (2)
 * Dry Bones (7)
 * Thwomps (3)
 * Cheep-Cheeps (3 green)
 * Boos (2)
 * Boom Boom (boss)

Level Statistics

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

Trivia

 * If the player enters the third door of the level, and repeatedly taps up on the before being dropped into the water below, Mario is taken to the boss room.