World 8-4 is the fourth and final level of World 8 in Super Mario Bros., as well as the final level in the game overall.
The final castle level consists of several Warp Pipes leading between rooms. One pipe in each area will take the player either to the next room or back to the start. If the player doesn't take a pipe, the room will loop around.
In the first area, the first Warp Pipe the player comes to is the pipe the player will exit from if they take the wrong ones up ahead. The next pipe will lead back to the start, and the pipe after that across a lava gap with a lift will lead to the next area. In the second area, the second pipe from the one the player exited from leads back to the start. The floating pipe up ahead leads to the next area, a Hidden Block is placed to the left of the pipe that acts as a platform to reach the pipe. In the third area, Cheep Cheeps will start jumping up from below. The second pipe from the one the player exited from leads back to the start. The pipe immediately after across a lava gap will lead to an underwater area with Fire Bars and Bloopers. The pipe at the end of the underwater area leads to the final room, with the only other pipe leading back to the start. After a Hammer Bro. followed by a Lava Bubble, the player will face Bowser, who throws hammers and breathes fire at the player character. Defeating him or touching the axe to destroy the bridge will allow the player to rescue the princess and complete the game.