The tower where the orcs take the stunned Frodo is the Tower of Cirith Ungol. It stands in Mordor near the mountain pass of Cirith Ungol and serves as a fortress guarding a route into Sauron’s realm.
After Shelob attacks Frodo, Sam initially believes his companion is dead and takes the One Ring. Orcs find Frodo and carry him into the tower, where they remove his mithril coat and argue over the valuable equipment. Their rivalry gives Sam an opportunity to enter the fortress and rescue him.
The tower is central to the final stages of Frodo and Sam’s journey in both J.R.R. Tolkien’s novel The Return of the King and Peter Jackson’s film adaptation. Cirith Ungol is sometimes confused with Orodruin, the volcanic Mount Doom, but the two locations are separate. Udûn is a region of Mordor, while Dol Guldur is a fortress in southern Mirkwood.