The Under-way was the left-hand side passage, delved by the Orcs, that led from the main tunnel in Shelob's Lair to the base of the Tower of Cirith Ungol. Near the main tunnel the passage was closed by the Undergate. Beyond the gate the passage wound, with constant twists and turns, to a final straight incline up to great brazen double doors that led to the deep chambers beneath the tower.
When Frodo and Sam first came upon the Under-way they were quickly stopped by the blocked Undergate. After Frodo was captured by the Orcs of the Tower, they took their prize through this passage. Sam, following them and wearing the Ring, listened through the gate and heard Shagrat and Gorbag talking, with Shagrat explaining that Frodo was not dead. As the orcs moved away, Sam drew Sting and saw that he could climb over the Undergate. He did so and tried to catch up with the orcs, but was confounded by the turnings of the passage. The orcs all entered the tower doors before Sam could get to the entrance, where he fell senseless in his attempt to crash through. When Sam awoke he traveled back down the Under-way to go by the main route to the tower.