Dr. Sudoku Prescribes #21 – Cave

Cave by Thomas Snyder


or solve online (using our beta test of Penpa-Edit tools; use tab to shift between shading mode and the linex mode where left click+drag draws lines and right click marks X’s)

Theme: “23” – Both today’s date, and a fine number for themed logic puzzles, such as the Map Puzzles from Bang 23.

Rules: Standard Cave rules.

Answer String: Enter the length in cells of each of the cave segments from left to right for the marked rows, starting at the top. Separate each row’s entry with a comma.

Time Standard: Cave Master = 3:00, Expert = 9:00, Novice = 30:00

Note: Advice on solving this puzzle (and Cave puzzles in general) has now been posted in “Ask Dr. Sudoku #4

Solution: PDF

Note: Follow this link for other Cave variations and this link for other classic Caves. If you are new to this puzzle type, here are our easiest Cave Puzzles to get started on.

  • Scott Handelman says:

    Nice puzzle, as always!

    Are there any future plans to allow sorting by solved/unsolved? It sure would be helpful!

  • skynet says:

    Very Sad that i am not able to solve this puzzle till now.Following are the genuine problems which i as a beginner face.
    i)There seems to be a confusion in my mind between the rules of Cave and Nurikabe.
    ii)The Notation that i m using in cave(shaded cells to represent caves and dots to represent unused cells )is not helping me very much.These notations are screwing me ,confusing me….I m going to use the reverse which i feel may be helpful.
    iii)I am not very sure whether i am completely aware of the rules of Cave.I read in motris’ Better know the USPC serice wherein i saw something abt an escape logic being mentioned.I dont think i m using that logic at all in this and the previous cave.Maybe thats why i am not able to solve this corral
    But i wont give up and i will try to complete this puzzle …..

    • Jack Bross says:

      First off, I think in the name “Cave”, we’re thinking of the part of the puzzle containing the actual numbers as the “cave” (and when you enter your solution by counting cave segments, that’s the part you count). For me, it’s easier to shade the part outside this region just because shading in the numbers makes it hard to read. Also, since the region inside the cave is all about sight lines, it makes a sort of intuitive sense for dark stuff to block the sight line of some unshaded stuff. Personally, with this sort of online puzzle, I just solve in MS Paint and shade both regions, but I make the cave itself light and the outside dark. (I use light blue and dark blue because I am very old and used to own a Commodore 64 and it makes me nostalgic 😀 )

      The “escape” strategy is because the part of the puzzle outside the cave must always connect to the outer edge of the puzzle. That’s because the actual cave isn’t supposed to be “donut shaped”. What that means is that if you end up with some shaded squares in the middle of the puzzle somewhere, and there’s only one route by which that shaded region can get out of the center, you can sometimes shade in some cells along the escape route.

    • Avatar photo drsudoku says:

      Just as with Tapa and some other types, I mark shaded with straight lines. And I’ll mostly circle the spent clues so I don’t come back to them, as here.

  • mokrton says:


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