Seems like there’s some interest, so lets do this. Going to dump a favorite, though I doubt it’ll last long.
You are trapped in a room with two doors. One of the doors leads out, the other to certain death. The doors are guarded by identical twin brothers. One of them always tells the truth, and one of them always lies. You do not know which is which. You may ask one question to one of the brothers. How do you determine which door leads out?