Waterline
(Published on 16. August 2026, 11:15 by varepsilon)
Normal Sudoku rules apply: Place the digits 1–9 exactly once in every row, column, and 3×3 box.
Waterline Loop:
Draw a single closed loop through cell centres, moving orthogonally. It must visit every non-5 cell exactly once and must not visit any cell containing a 5.
Along each maximal straight segment of the loop, including the turning cells at both ends, the digits must strictly increase or strictly decrease from one end to the other.
At each turn, the digit must be either a valley (1–4 and lower than both adjacent digits on the loop) or a peak (6–9 and higher than both adjacent digits on the loop).
Solution code: Digits in row 4, read from left to right.
Comments
on 24. August 2026, 05:24 by SudokuHero
I agree with LMDemasi, this puzzle is closer to a 3* than a 4*. Really enjoyable puzzle I love the way you have constructed it. Really nice breath of fresh air after consuming a ton of slop recently.
on 23. August 2026, 14:49 by Piatato
Awesome! Cool ruleset, and a very smooth solve!
on 17. August 2026, 12:21 by lmdemasi
This was an excellent puzzle. The loop rule was interesting and had a couple of nice nuggets to work out about how it worked.
The loop rule looks a bit intimidating at the start, but I found it very intuitive when you start applying it and I think the puzzle is quite approachable. I would say 3* rather 4*.
on 17. August 2026, 05:10 by Allagem
Great execution on an interesting concept - loved it!
For completeness, the Waterlines here is reminiscent of summit lines by Vythic, where digits alternate ascending and descending along a summit line but the direction can only reverse on the digit 1 or 9. In this puzzle, the ascension reversal is more constrained by geometry, which is a fun twist :)
