Building World is a world in Mario's Early Years! Fun with Letters. It is one of the seven islands in the game and is represented by a pair of building blocks.
The world takes place in a area of pipes and a background of puzzle pieces.
The player will be given the command to find the block that contains the required word sound. These fit into a 2X2 puzzle and when the player completes said puzzle, they can proceed to the next level The third level requires you to complete the word shown. When the correct answer is given a random character or creature pops out of the scenery praising the player.
The world is different in the PC version as it revolves around sounding out words commonly found at a baseball game. Various animations occur when the cast is clicked on.