This trap is a cunning one. A key passage had a cul-de-sac built onto it during the initial construction. Once it was completed, the resident arch-mage cast a powerful enchantment over the intersection of the cul-de-sac, and the main passage. It was a simple, yet effective illusion that caused the party to deviate into the cul-de-sac. The illusion gave the impression of an endlessly long passage that could not be escaped by returning by the way they came. In essence, the party would be left to run itself to exhaustion, or even death as there was no escape from the powerful illusions.
The Key:Fifty steps from the eorlingas/guided by that which is sinister/Through dreaming eyes
What it means: The junction of the passage is marked by a painting of an unknown and obscure man. He was once an eorl of a lost kingdom. There are other paintings along the wall. Fifty steps is the length of the intersection of the two passages. The Arch-mage who created the schematics for the trap was left handed, and sinister refers to the left hand and dexter refers to the right hand, thus mbidexterity literally means both right hands. Placing the left hand on the wall as a guide keeps the PC on the right path. Dreaming eyes are closed.
Close your eyes, left hand on the wall, count 50 steps. you are past the trap.