Cirith Ungol, also known as the Morgul Pass, was the pass through the western mountains of Mordor and the only way towards the land from the west.
It was guarded by the Tower of Cirith Ungol, built by the Men of Gondor after the War of the Last Alliance of Elves and Men was fought.
During the War of the Ring, Frodo Baggins and Samwise Gamgee were led to this pass by Gollum to the lair of the giant spider Shelob who dwelt there.
It is not known whether the pass and the tower were called Cirith Ungol when the Men of Gondor held it since Shelob could not have inhabited the cavernous entrance of the pass at that time.
Cirith Ungol (pron. [ˈkiriθ ˈuŋɡol]) is a Sindarin name meaning "Spider's Cleft", composed of cirith and ungol.