Here is a riddle that requires some thinking...
After his death, a man encounters a gateway that has two large doors at the end. One of the doors leads to Heaven, and one of the doors leads to Hell. Each door has its own guardian. The "Guardian of Heavenly Truths" always tells the truth, and protects the door to Heaven. The "Guardian of Hellish Lies" always tells lies and protects the door to Hell. Both of the doors look exactly the same, and both of the guardians look exactly the same. In order to figure out which door leads to Heaven, the man has to ask only one question, a yes-or-no question, to one guardian of his choice. Afterwards, he has to choose which door he must permanently enter. The man smiles and asks a random guardian a yes-or-no question. With confidence, the man ends up choosing the door that leads to heaven.
What question did the man ask one of the guardians?