(Some of you may already know the answer, so please just write a solution, if you never heard of this riddle)
You are in a room. In there are two doors. Behind one is the thing you always wanted to have, whether it's money, fame, family, it waits behind that door. Behind the other door is unbelievable horror. If you open that door, you will see things that will haunt you for eternity.
In front of the doors, there are two guards. You know that one of them is always telling the truth, the other one is always lying. But you don't know who is doing what. They will answer you one single question together.
Which Question do you need to ask, to make sure which door is the correct one?