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I recently heard a version of the classic two guards (one is a knight who always tells the truth and the other is a knave who always lies) standing by two doors (one leads to certain death and the other to life) with a tiny twist that makes it much better, in my opinion, for younger audiences.

You come to a fork in the road. One path leads to a village of knaves where you will be killed and the other to a village of knights where you can live happily ever after. There are two people standing by the road, a knave from knavesville who always lies and a knight from knightsville who always tells the truth, but you do not know who is who. You can ask one of the people one question. What do you ask and what do you do?

All the answers from Two doors with two guards - one lies, one tells the truth will work here, but there is an additional answer that works in this situation that does not work in the classic telling. What I like is that this additional answer (i.e., question) does not need to have a double negative or be a multi-part question and is a rather simple question.

I think what makes it different is

that the knight is from knightsville (where you want to get) and the knave is from knavesville (where you want to avoid).

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    $\begingroup$ Is this different enough from: puzzling.stackexchange.com/questions/2188/… $\endgroup$
    – Dorrulf
    Commented Nov 26, 2018 at 21:49
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    $\begingroup$ @Dorrulf all the answers from that question work, but there is an additional answer that works for this riddle. $\endgroup$
    – StrongBad
    Commented Nov 26, 2018 at 21:50
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    $\begingroup$ @RobertS. I just edited the question. There is an answer that works for this question that does not work for the duplicate one. I think that makes it unique. $\endgroup$
    – StrongBad
    Commented Nov 26, 2018 at 21:53
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    $\begingroup$ I guess I mean I don't understand what the difference between the two is. Reading through, they seem to be the exact same thing to me. Can you help me understand the difference between your question and the linked one @StrongBad? $\endgroup$
    – Dorrulf
    Commented Nov 26, 2018 at 21:54
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    $\begingroup$ For targeting younger audiences, you probably want to dial down the murdering a bit, too. Something along the lines of "Knights will give you free food and shelter for the night, and knaves will charge you double the reasonable rates" should be quite enough of an incentive for this puzzle. $\endgroup$
    – Bass
    Commented Nov 26, 2018 at 23:49

2 Answers 2

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The other answer is

Which path leads to the city you're from?

The knight will answer with the path pointing to Knightsville, and so will the knave.

However, this assumes that the knave does not lie by saying "Neither", or giving some unrelated answer.

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    $\begingroup$ (Note: This is effectively the same as one of the original answers (making the assumption given in my answer), but a nice stipulation in this version of the problem makes it shorter and more natural to phrase.) $\endgroup$
    – Deusovi ♦
    Commented Nov 26, 2018 at 21:59
  • $\begingroup$ Well, that assumes also that they will [cbvag] when you could also perhaps [nfx gurz gb fnl be gryy lbh]. At that point, it probably doesn't matter what answer the knave gives either, related or not. $\endgroup$
    – Dorrulf
    Commented Nov 26, 2018 at 22:06
  • $\begingroup$ However you can choose a path and ask one whether this certain path leads to his home-city. That doesn't leave logical options for the knave to fool you. $\endgroup$
    – Thomas Blue
    Commented Nov 27, 2018 at 11:17
  • $\begingroup$ ... and you reach the city of knights, confident, you greet a knight who in return pushes his sword through your chest. Dying, you say "But knights don't kill!". The knight smiles and says "Who told you that?". $\endgroup$
    – Florian F
    Commented Aug 18, 2020 at 15:40
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Here is what I think.

There are two doors; there are two guards; one lies; one tells the truth. You would have to simply ask this question.

To the guard who tells the truth: if I were to ask the guard who lies, which door would he tell me to enter?

Since he can only tell the truth, he would give you the answer that the liar would tell, therefore you open the opposite door and make your way to heaven.

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