Cave Sums Sudoku
(Published on 2. January 2026, 20:39 by Christounet)
This puzzle was meant to be part of a larger gift for the Secret Satan event, so it contains a couple devilish deduction that require intricate arithmetics. Overall, it should be between 4 and 5 difficulty. I put a hidden comment to fully explain my solve path of the hardest deduction, for anyone interested. Have fun!
The puzzle :
Rules :
- Normal sudoku rules apply
- Cave: Shade some cells such that all unshaded cells are orthogonally connected to each other and all shaded cells are orthogonally connected to the edge of the grid.
- Clued cells are ambiguous.
- A number in a shaded cell gives the sum of the digits in all shaded cells connected to that cell, including itself.
- A number in an unshaded cell gives the sum of the digits seen in all unshaded cells seen from that cell vertically and horizontally, including itself. Shaded cells block vision.
- Digits may repeat in the sums if allowed by other rules.
- A ? represents a digit from 1-9.
Example puzzle :
Solution code: Digits in unshaded cells in row 6 and column 6.
Comments
on 6. January 2026, 21:33 by War
Excellent puzzle! It's reassuring to see that my solve path was the same as intended.
on 5. January 2026, 18:58 by henrypijames
Yeah, only 3½ difficulty for me as well. May just be luck, but I got all the pressures on that difficult clue right away.
A very general hint for this puzzle would be: no checkerboard, no checkerboard, no checkerboard in cave puzzles!
on 4. January 2026, 13:36 by samuel1997
Very cool puzzle, and actually it is not that hard, surprisingly.
on 3. January 2026, 14:20 by Myxo
Beautiful!
on 3. January 2026, 13:00 by Snookerfan
Brilliant puzzle! Some very interesting logic in there. Thanks
on 3. January 2026, 08:28 by Christounet
Reformulated the definition of a clued shaded cell.
on 3. January 2026, 03:31 by KNT
Wow, getting started was super hard.
on 3. January 2026, 02:01 by Piatato
Delightful!
on 2. January 2026, 22:33 by cyddrdrd
Very cool! Love how the arithmetics work at the beginning!
on 2. January 2026, 20:55 by isajo4002
Easy peasy solved it in under 10 minutes
