There is a popular logic puzzle often referred to as “The Doors to Heaven and Hell” or “The Two Gates” riddle. It goes something like this:
You find yourself standing in front of two identical doors. One of these doors leads to Heaven and the other to Hell. Next to each door is an identical guard, only capable of communicating by pointing, indistinguishable from each other except that one always tells the truth, the other always lies. You, unfortunately, do not know which is which, of neither the door, nor the guard. You can pose only one question to one of them in order to find the way to Heaven. What question do you ask?