Battle of Helm's Deep

The Riders turned south along Deeping Stream some 15 miles short of the Fords of Isen.
The Wall curved round the fortress and the road came in by a long ramp over the stream.
Some quarter of a mile further out was the mile-long dike and rampart. (Helm’s Deep; Bk 2).

Death Down, where the fallen Orcs were buried, was a mile from the dike. (The Road to Isengard; Bk 2).
The path shown leading south and up into the hills was the road taken by Theoden and his Riders, with Merry,
after leaving Isengard, to summon the mountain men to the Muster of Rohan at Dunharrow.
(The Passing of the Grey Company; The Muster of Rohan; Bk 3).

Thrihyrne ('Three Horned [Peak]') -- The name given in Rohan to the tall, triple crowned mountain which lay to the south of Aglarond and Helm's Deep.
Helm's Deep was in fact a ravine in the northern face of the Thrihyrne.