In The Lord of the Rings: The Two Towers, Aragorn helps defend Helm’s Deep during the Battle of the Hornburg.
Helm’s Deep is a fortified valley in Rohan, while the Hornburg is the fortress at its inner end. The film commonly uses “Helm’s Deep” for the entire defensive location, which is why that is the familiar answer to this question. Théoden leads the defenders, with Aragorn, Legolas, Gimli, and a small force of Rohirrim and other allies.
Saruman’s Uruk-hai army attacks the fortress at night. The battle features the explosive breach in the Deeping Wall, the defense of the outer defenses, and the final charge led by Théoden and Aragorn. Gandalf’s arrival with Éomer and additional riders turns the battle’s outcome.
Helm Hammerhand, an earlier king of Rohan, gives the location its name. The fortress was filmed mainly at Castle Hill in New Zealand.