World 3-4 (Super Mario Bros.: The Lost Levels)

World 3-4 is the fourth and final level of World 3 in Super Mario Bros.: The Lost Levels, taking place in a castle.

Layout
The layout of this level is a maze, and the player has to go through the correct path in order to progress. If the player chose the incorrect path, they will have to repeat the same area until they choose the correct one.

After the second lava pit, the player needs to take the path on the bottom, avoiding a third lava pit, and jump over the pipe with a Piranha Plant. The next path is the one on the bottom, though the player can only legitimately move through it if they are in a small form; if they are not in small form, they can get hit by the previous Piranha Plant. A Lava Bubble also jumps up from the pit ahead, and the player can find a Hidden Block with a power-up between the second array of gaps in the platforms.

The path can also be traversed as Super or Fire Mario through a series of well-timed crouches. In Super Mario Bros. Deluxe, the path above it is also correct, eliminating the problem altogether.

For the second puzzle, the player needs to jump over the two pipes with Piranha Plants and find four Hidden Blocks on the lower path afterward, or use the first pipe to reach the upper platform. Using these blocks as a platform, the player can reach the upper paths which they must remain on, avoiding the Fire Bars ahead. Afterward is the Fake Bowser with a Lava Bubble jumping up from below.