You are lost in the woods and the path you are following forks into two: a path to the left and one to the right. One path will lead you to safety while the other will cause you to be lost forever.

At the fork are two twin sisters who know which path is which. The sisters are identical in every way except one: one of the sisters always tells the truth while the other always lies.

You can ask only one question and you don't know which sister is which. What can you ask them so you know which path to take?

What would your sister say, which path leads to safety?

Explanation:

"The identical twins" is a famous riddle in many countries and with many variations, but the core remains the same; one twin always lies, the other one always tells the truth.

So, the correct question to answer would be: "What would your sister say, which path leads to safety?", and whatever answer may be, you always take the other path.

Let's make the presumption that the right path is towards safety. If you ask the truth-telling twin what would her sister say, she knows that her sister would lie and that she would say the left. Since she always tells the truth her answer would be left.

If you ask the lying sister the same question, she knows that her sister would say the right way, but because she lies, her answer would be the left.

So, both sisters will answer identically to this question so the only thing to do now is to take the another path.