What is the riddle where one has to find which door Heaven and Hell with Angel telling truth Skeleton lying?

You are in a room with two doors and two guards. One of the doors leads to heaven, and the other to hell. Each guard is assigned to one of the doors, but one of them always tells the truth, and the other always lies. You don't know which guard is telling the truth or who is assigned to which door. You may only ask one question to one of the guards. What should you ask to determine which door to take?

Answer:

Ask one of the guards: "If I asked the other guard which door leads to heaven, what would he say?"

Here's the logic behind this question:

* If you ask the honest guard, he will correctly tell you what the lying guard would say, which is the door to hell.

* If you ask the lying guard, he will give you the opposite answer of what the honest guard would say, which is also the door to hell.

Therefore, regardless of which guard you ask and whether they are honest or lying, the answer you receive will always be the door to hell. So, the other door must be the door to heaven.