A man comes to a fork in the road. One road leads to ultimate happiness and the other leads to never ending torture. There is a house right in the middle of the fork. A sign in front of the house reads: Twins live here; one always tells the truth and the other always lies.
The man reads the sign and knocks on the door. One of the twins answers.  The man asks him a single question and then takes the road to ultimate happiness.
What is the question that he asked?
The man asks:
Which road would your brother tell me to take?
Whatever the answer, the man chooses the OTHER road and proceeds.