Cirith Ungol
Cirith Ungol, meaning the Pass of the Spider in the Elvish tongue, is a high and perilous pass through the Mountains of Shadow (the Ephel Dúath) on the western border of Mordor, above the haunted valley of Minas Morgul. It is a secret and dreadful way into the Dark Lord's realm, guarded by the monstrous spider Shelob in her lair and overlooked by the orc-tower of Cirith Ungol. It is by this pass that Frodo and Sam, led by Gollum, seek to enter Mordor unseen.
Cirith Ungol is one of the most harrowing stages of the Ring-bearer's journey, a place of darkness, treachery, and despair, where Frodo is poisoned and taken and Sam must take up the burden alone.
Geography
The pass climbs from the valley of Imlad Morgul, above Minas Morgul, by a long stair, the Straight Stair and the Winding Stair, cut into the mountainside, and then runs through a high cleft toward Mordor. Near the top, the way passes through the lair of Shelob, a maze of tunnels filled with foul webs and reeking darkness, called Torech Ungol. Beyond the lair and the cleft stands the Tower of Cirith Ungol, an orc-fortress built by Gondor in former days to watch Mordor but now held by the enemy, guarding the descent into the land beyond. From the pass one looks down at last upon the plain of Gorgoroth and the fire of Mount Doom.
History
The Tower of Cirith Ungol was raised by the Men of Gondor after the fall of Sauron in the Second Age, to keep watch upon Mordor lest the evil return. But as Gondor's strength waned and Sauron crept back, the watch failed, and the tower fell into the enemy's hands, becoming an orc-hold guarding the pass it had once warded against. The great spider Shelob, last child of an ancient evil from the Elder Days, made her lair in the tunnels of the pass, devouring orcs and any other prey that came her way, and even the orcs feared her.
In the story
Gollum leads Frodo and Sam to Cirith Ungol, intending to deliver them to Shelob and recover the One Ring for himself. In the dark tunnels Shelob attacks; Sam drives her off with the Phial of Galadriel and the sword Sting, wounding her, but Frodo is stung and falls as if dead. Believing his master slain, Sam takes the Ring to carry on the quest, only to learn that Frodo lives and has been captured by the orcs and borne into the Tower of Cirith Ungol. Sam fights his way into the tower, finds it strewn with the orcs who have slaughtered one another over loot, and rescues Frodo, and together they pass on into Mordor toward Mount Doom.