The Prince's Pass is the largest pass through the Red Mountains, linking Dorne to the Stormlands and the Reach. It is the main overland route between Dorne and the rest of the Seven Kingdoms. It begins south of Nightsong and proceeds southwards through the mountains into the north-west of Dorne, emerging near Skyreach.
In the books
In the A Song of Ice and Fire, the Prince's Pass is the main trade and travel artery between Dorne and the rest of the continent. It is also a natural choke-point in times of war, and prevents easy access for armies from other parts of the continent into the Dornish interior. The military value of the pass was even enough to stymie Aegon the Conqueror's invasion of Dorne, with his dragons unable to be deployed effectively against an enemy fighting from behind rocks and in ambushes.
Daeron I, the Young Dragon, used this to his advantage when he invaded Dorne one and a half centuries later. After sending an army into the pass, drawing the Dornish forces out to defend it, he landed a substantial second army by sea at the mouth of the Greenblood, effectively outflanking the entire nation and compelling the Martells to surrender.
Ninety years before the events of the novel, a bandit lord known as the Vulture King seized control of the northern part of the Prince's Pass. Houses Caron and Dondarrion made an alliance and sent troops into the pass to root out the Vulture King. Duncan the Tall accompanied this expedition.
House Fowler of Skyreach serves the Prince of Dorne as the Wardens of the Prince's Pass, and are entrusted with its defense.
The other, less well-used pass through the Red Mountains is known as the Boneway.