Hard 16x16 Sudoku demands the full note-taking discipline of a hard 9x9, multiplied by sixteen symbols. Naked triples, X-Wings and box-line eliminations are routine, and the grid rewards players who work region by region instead of chasing digits at random.
Rated 3.0–4.9 by Sudoku Explainer, hard giant puzzles typically take well over an hour. Use note mode, lean on undo, and let autosave hold the board between sessions. Compare the variants in our types of Sudoku overview.