Which guard is telling the truth?
Thereof, who is telling the truth riddle?
One of the doors will guide you to freedom and behind the other is a hangman --you don't know which is which. One of the guards always tells the truth and the other always lies. You don't know which one is the truth-teller or the liar either.
Also to know is, what is the answer to the two doors riddle?
The simple answer is to ask either one what the other guard would say and go through the opposite door. But that won't work. If the first guard is telling the truth about one of them always telling the truth the other guard must lie so "one of us speaks only lies" must be a lie.
The riddle: One door leads to good things, the other to bad things. You can only ask one guard and one always tells the truth and one always lies. You have to ask the right question in order to figure out which is which. Breaking this riddle down to facts is that you have two guards.