Lord Commander Mormont tells Jon Snow that the legendary Qhorin Halfhand had to spend the whole previous winter beyond the Wall, as he was north of the Skirling Pass when the snows came and he wasn't able to go back until the thaw. During the Great Ranging, Qhorin takes a small scouting party —consisting of himself, Jon Snow and a few other men— into the Skirling Pass to attack the lookouts posted there by Mance Rayder, the King-Beyond-the-Wall. Ygritte later shows Jon Mance's massive camp, located in the pass.
In the books
In the A Song of Ice and Fire novels, the Skirling Pass is named for the keening sound the wind makes as it blows through it. The pass has been a traveling and trading route for millennia. An ancient stone archway is located at the top of the pass. A large glacier and a frozen lake are located at either side of a hidden valley near the top of the pass, where Mance Rayder's army made camp.