The Comb is the range of steep hills along the Rethwellan-Valdemar border. The terrain is terrible for traveling in the best of times, and is frequently quite deadly in the winter. In description:
"The hills themselves weren't all that high--but they were sheer rock faces for the most part, with little more than goat tracks leading through them, and not much in the way of vegetation, just occasional stands of wind-warped trees, a bit of scrub brush, rank grasses, and some moss and lichen..." (Oathbreakers)
The vegetation is just barely enough to keep a horse alive, and travelers do better to bring grain with them.