20. The fork in the road
1. Ask either of the twins, "If I asked your brother the way to Eldorado, which road would he tell me to take?"
If you're talking to the truthful brother, he’ll direct you to the road that the lying brother would indeed recommend – which would be the WRONG road.
But if you're talking to the lying brother, he’ll also point to the wrong road; he’d lie and point you to the road that the truthful brother would NOT recommend.
Either way, you’ll know to take the other path.