You are at a crossroad. One road goes to hell, the other to paradise. There is one guard. The guard only answer questions and only using Yes or No. The guard is one of two categories: one category always lies, the other always tells the truth (but you don't know to which category the guard belong). You are allowed to ask only one question to decide which road to take.
Can you ask a single question to the guard and be sure to go to heaven? Note that you cannot ask about what another hypothetical guard could answer because you do not know which kind she or he could be.
This question differs from the two guard question because there is only one guard. You cannot refer to another guard.