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Near the main tunnel the passage to the Under-way was partially blocked by a great stone that was shaped like a heavy door. The stone was less than twice the height of Sam with a blank space between the top of the stone and the ceiling of the passage so that Sam was able to climb over it. Beyond the stone was a bend and then a winding passage with a final straight incline up to great brazen double doors that were called the Undergate, which led to the deep chambers beneath the Tower of Cirith Ungol.
When Frodo and Sam first came upon the Under-way they were quickly stopped by the stone that blocked the entrance to the Under-way. After Frodo was captured by the Orcs of the Tower, they took him 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 stone. 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 travelled back down the Under-way to go by the main route to the tower.
 Portrayal in adaptations
- The The Tower of Cirith Ungol and Shelob's Lair adventure module contains a floor plan of Shelob's Lair that includes the Under-way (spelled Underway there), a description of the mechanism to open the stone block, floor plans of eleven levels of the Tower of Cirith Ungol with the Undergate located on the first level on the side that faces the mountain side and a description of the Undergate in T.A. 1640. It mentions that the Tower of Cirith Ungol is still manned by a Gondorian garrison in T.A. 1640 until the end of the second millennium of the Third Age when the Tower of Cirith Ungol was left uninhabited by the Gondorians.