The Lands of Ice and Fire places the site of the battle between Riverrun and Oldstones, west of Fairmarket and south of the Blue Fork of the Trident. The non-canon map for HBO's Game of Thrones places the wood south of the Blue Fork and north of Raventree Hall.
A rocky stream runs through the forested valley; its northern end narrows and bends like a cocked elbow. The trees are thick enough to block most moonlight. Snow shrikes live in the Whispering Wood.
A Game of Thrones
A Storm of Swords
While journeying north from Riverrun to the Twins for the wedding of Ser Edmure Tully and Roslin Frey, Robb's army passes again through the Whispering Wood. Most of the leaves have changed from green to dull gold, brown, and red, but spruce and soldier pines still show green. Catelyn Stark sees remnants of the battle from early in the War of the Five Kings, including bones, weapons, armor, and stone cairns.
Here was a hush in the night, moonlight and shadows, a thick carpet of dead leaves underfoot, densely wooded ridges sloping gently down to the streambed, the underbrush thinning as the ground fell away.—thoughts of Catelyn Stark