The "World's Tallest Crossword" game mode presents a new grid of larger (13x13 square), more challenging puzzles to complete.
This mode works slightly differently to the original World's Biggest Crossword grid. Puzzles become available to unlock in groups, and you must complete all the crosswords in the current group before the next group becomes accessible. Each completed group increases the height of the tower.
This mode can be accessed from the Main Menu after the first puzzle section of the World's Biggest grid has been completed.
You can return to the Main Menu from anywhere in the game by selecting the Pause Menu (the gear icon in the top right corner of the game screen), and selecting 'Main Menu'.