You approach two talking doors. One door leads to the City of Truth, while the other door leads to the City of Liars. You do not know which door is which. You are able to ask only one question to determine which door is which. The door that leads to the City of Liars always speaks lies, while the door that leads to the City of Truth always speaks the truth. You want to go to the City of Truth. What question do you ask to determine which door leads to the City of Truth.

This riddle does not have 2 guards, You can only ask one question to determine which door to go through.

You are asking a door, the door will reply to you, But you can only ask one of the doors.

  1. The Truth Door

  2. The Liar Door


Ask a question that will involve both doors.

  • $\begingroup$ I updated my post! @athin $\endgroup$
    – dumbgeek
    Mar 28, 2018 at 16:42
  • $\begingroup$ Hmm.. But doesn't it still have the same solution? (Just replace the guard with the door, cmiiw.) $\endgroup$
    – athin
    Mar 28, 2018 at 16:46
  • $\begingroup$ No, Lemme update my post again! $\endgroup$
    – dumbgeek
    Mar 28, 2018 at 16:47
  • $\begingroup$ Post updated @athin $\endgroup$
    – dumbgeek
    Mar 28, 2018 at 16:53
  • $\begingroup$ IMO, even if this isn't a duplicate, it's too broad. The original specifies that you have to ask a yes/no question, but this one doesn't, so you can literally ask any question to which you already know the correct answer. $\endgroup$
    – F1Krazy
    Mar 28, 2018 at 16:56

2 Answers 2


Even with the edit, this is still effectively a duplicate, but all of the answers to that question are overly complicated, so I will post my own here:

You should ask either door:

What is 1+1?
The door that leads to the city of truth will answer 2, and the other door will answer something else, so you'll know which is which.


I think the intended answer is (based on several variations I've heard) is

Ask either door "which door would that door tell me to go in?" Both will say the same door for opposite reasons. You then choose to go through the other door.


Not the answer you're looking for? Browse other questions tagged or ask your own question.