EPHEL DúATH

In J. R. R. Tolkien's fictional world of Middle-earth, the 'Ephel Dúath' or 'Mountains of Shadow' are a range of mountains that guard Mordor's western and southern borders. Their Sindarin name means literally "outer fences of dark shadow". They meet the Ered Lithui at the Morannon (Black Gate), so that between them the mountain ranges effectively seal off Mordor from invasion on three sides. The city of Minas Morgul defends its largest pass, often called the "Nameless Pass", containing the cursed river Morgulduin.
A partly hidden stair leads from the north bank of the Morgulduin, up to a high pass of Cirith Ungol. That leads through the Ephel Dúath from the Stairs of Cirith Ungol behind Minas Morgul to the Tower of Cirith Ungol. Also the castle of Durthang was located in Ephel Dúath.