TheYellowCellPhone said:
You walk down a path to a City of Truth and the road splits. One leads to the City of Truth, the other to a City of Lies. You know if you go one way, it will be too late to turn around.
However, at the split there are two men, one at each road. One is from the City of Truth, and will only tell the truth. The other is from the City of Lies, and will only lie. You don't know which man if from what city.
So, what do you ask them? I know one answer.
Simple - ask them any factual question. The liar will always lie and thus will claim that, for example, 2+2=3.
Now if you'd have said that one will always tell the truth, but the other one is not averse to lies, then it would be a different matter and, in fact, it would be unsolvable. Free will fucks up most riddles.