There are two doors. One goes to Heaven and one goes to Hell. Neither of the doors are identified as being Heaven or Hell.
There is a guard standing in front of each door. The two guards are identical in every way, except that one always lies and one always tells the truth. You don't know which one lies or which one tells the truth.
If you wanted to walk into the door of Heaven and had one question to ask either of the guards, what would it be?
--I couldn't figure it out.