World 7-Fortress 2
From the Super Mario Wiki
World 7-Fortress 2 is the second fortress level and twelfth level overall of Pipe Land in Super Mario Bros. 3. The level becomes accessible upon completing World 7-9 and its own completion unlocks World 7- 2.
The main hall of this level is made up of many pipe platforms situated over lava. Many of the pipes have Piranha Plants or Venus Fire Traps in them, and Boos are placed between some of the pipes. One Roto-disc and two Thwomps also act as obstacles. In the first Brick Block, the player can find a Starman, and a power-up in the ? Block near the middle of the room. To land on the pipe at the end, the player has to fall off the above platform while pressing left on the to avoid falling into the lava.
The second room is another long hall, this time consisting of several Roto-discs and Thwomps. If the player is powered-up, the player will have to slide under a wall while avoiding both traps. At the end of the hall is Boom Boom, who will open up a nearby gate on the map upon being defeated.