A brainy question, try it out
You are at an unmarked intersection ... one way is the City of Lies and another way is the City of Truth.
Citizens of the City of Lies always lie.
Citizens of the City of Truth always tell the truth.
A citizen of one of those cities (you don't know which) is at the intersection.
What question could you ask to them to find the way to the City of Truth?
First ask him, Which side the road that you are coming goes?
If he tells correct than you can trust him and ask the road to city of truth.
But if only question is to be asked than have to think.
Broke the rule:
Googled and got this answer
You ask "In which of those two directions do you live?"
A Citizen of the City of Lies will point to the City of Truth
A Citizen of the City of Truth will point to the City of Truth