So, I've finished building my "Island of Logic!", where there are a number of puzzles for travellers. So far, I have a bunch of rivers with river craft, wolves, goats, and cabbages; and a number of areas with people who always lie and others who always tell the truth. There's also a sudoku room, and a few other similar places.

Of course, there is the classic "two doors, two guards" room, but since this is a tourist destination, and I actually want return visitors, the "bad door" leads to a room with nothing but sofas (but no coffee) and another exit, and the "good door" leads to the souvenir shop and cafe (which has sofas and coffee) and another exit.

During my final inspection before opening to the public, I found a problem: One of the guards from the "two guards, two doors" room had been working a double shift in one of the other knight/knave areas, and has had to take some time off. I'm not sure which guard it was, and I don't really want to ask the other one... No matter! The opening weekend must go ahead.

So, what I need from you, is this: what question do I ask the one remaining guard to get to the souvenir shop, and when the guard points to a door, do I take it, or take the other?

(Attribution: The two doors/two guards is extremely well known, and I don't know the origin. As far as I am aware, this variant is mine, but I wouldn't be surprised if someone else has also created it before).


There are two doors, one of which you want to use, the other you don't. There is one guard, who might be a knight (always tells the truth), or a knave (always lies). You may ask one question, and then must take a door. What's the question?

  • $\begingroup$ This exact question as been asked here before. That was closed as a duplicate of the standard version because several of the answers to that standard one also work for this single guard variation. $\endgroup$ Commented May 18, 2023 at 6:54
  • $\begingroup$ @JaapScherphuis I'm not really surprised it has been asked before, but a quick search didn't turn it up. I thought it might be novel enough, but I understand if this one gets closed as duplicate. I can just delete the question, if that's better; just let me know. $\endgroup$
    – enkorvaks
    Commented May 18, 2023 at 7:11
  • $\begingroup$ On other sites, duplicates are usually left there so that someone doing a search can find the answer if their search matches any of the existing wordings for the question. On puzzling, where searching for an original puzzle is unlikely, leaving duplicate postings around feels like clutter. It probably won't be deleted for you, but feel completely free to delete it yourself. Have a lovely Puzzling day! $\endgroup$
    – Rubio
    Commented May 19, 2023 at 21:26


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