Oak Sudoku

Rules

Warm wood, dark grain, digits carved rather than printed. Every placement is a hollow wooden knock — the sound of a wooden tile set down on a table.

• Each row, column and 3×3 box holds 1–9 exactly once — no extra rules.
• Placements knock: dry, low, with a short wooden tail.
• A finished unit gives a deeper knock and a longer body.
• Three difficulties, hints available, progress saved in this browser.

Good to know

Ordinary sudoku rules still apply underneath the variant: every row, column and 3×3 box holds 1–9 exactly once. The extra rule sits on top and is usually what breaks the puzzle open.

More sudoku

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Or read how to play Sudoku ↗.