The truth or a lie ?
You are on you way to the city (to get some food and fun).
At some point in time the road splits itself and you have to stop. You don�t know which way to go.
After waiting some time two identical twin sisters come down the road. You recognize them and remembers that one always tells the truth, while the other always lies.
What ONE question would you ask to know which way to go to the city ?
< no, you did NOT bring a lie detector ;-) >