Cirith Ungol

Cirith Ungol was a pass or cleft through the Ephel Dúath located near Minas Morgul. At its heart was an Orc stronghold, near the caves of Shelob's lair.

History
Under Gondor
Cirith Ungol passed through the western mountains of Mordor and paralleled the Morgul-road into Gondor to some degree. It was guarded by the Tower of Cirith Ungol, which was built by the Men of Gondor after the War of the Last Alliance was fought. It is not known whether the pass and the tower were called Cirith Ungol when the Men of Gondor held it, though it is likely since Shelob "...was there before Sauron, and before the first stone of Barad-dûr" was laid, and Cirith Ungol meant 'Spider's Cleft' in Sindarin.

 
The pass was reached by several sets of steep stairs leading from close by Minas Morgul up the north cliff-face of Morgul Vale and through a tunnel high in the mountains, with other steep stretches that lacked stairs. Eventually, the path ran straight into Shelob's lair, though many side-tunnels had been carved by Orcs and Men to get past her webs.

 
Under Sauron
Gondor occupied the tower guarding the pass until TA 1636 when the Great Plague killed much of Gondor's population. After the Plague, Gondor again occupied Cirith Ungol but they were eventually distracted by the Wainriders, and evil was allowed to return to Mordor. The tower was likely occupied by evil forces before Minas Ithil was besieged in TA 2000.

In the Quest of the Ring, Frodo Baggins and Samwise Gamgee were led to this pass by Gollum to the lair of the ancient spider Shelob. At this time, there were also three-headed statues that "watched" the gateway into the keep of Cirith Ungol which could not be passed by mortals. Only through use of the Phial of Galadriel could the ring-bearer and his servant break these entities' will and enter.