This is the same scenario from the movie Labyrinth starring David Bowie. The girl in the Labyrinth solves the riddle by asking one (guy 1) of the "guys" the following question: "If I asked the other guy (guy 2) if the path to the right is the correct path, would he tell me that it is?"
Here are possible scenarios based on guy 2's response:
1) "yes", guy 2 always tells truth - Invalid condition
2) "yes", guy 2 always tells lies - path on left
3) "no", guy 2 always tells truth - path on right
4) "no" , guy 2 always tells lies - path on right
Therefore if guy 2 says "yes", then take path on left. If he says "no", then take path on right.