You are trapped in a dungeon, and see two doors in front of you. One is a way out, andther will lead to certain death.
Two people are standing in front of these doors, one of them a Knight, another - a Liar. Naturally, you do not know who is who, but they know each other's true nature.
Both the people know which way is correct, but you can only ask one question of one of them before making your choice.
What will you ask?
Point to either door, and ask either person: "If I'd come here earlier, and asked if this were the way out, would you have told me it was?"
If answer is "Yes," it's correct door, whether you've asked of either the Knight or Liar (and you don't care).
If "No," the other door is the way out.
Different question
