The fortress where Helm’s Deep lies in J.R.R. Tolkien’s The Lord of the Rings is the Hornburg.
The Hornburg is a stronghold in the valley of Helm’s Deep, in the western part of Rohan. During the War of the Ring, King Théoden and the defenders of Rohan retreat there while Saruman’s forces attack. The fortress and its defensive wall become the setting for one of the story’s major battles.
Helm’s Deep is the name of the valley and surrounding defensive area, while the Hornburg is the fortress itself. These names are often used interchangeably in casual discussion, but Tolkien’s geography distinguishes them.
Minas Tirith is the principal city and fortress of Gondor. Isengard is Saruman’s fortified base, and Barad-dûr is Sauron’s tower in Mordor. Neither is located in Helm’s Deep or belongs to Rohan’s defensive complex.