The Ancient Passage lies at the northernmost point of the Veiled Stair. It is a large cave with a large river running through it. A ferryman will allow passage on his boat through the passage and into Kun-Lai Summit, though it appears traversing the shore is also possible.
This is ill-advised; the cave is filled with high level saurok and players are dismounted upon entering. However, if players are attempting to reach the Secret Aerie, walking through the passage is the only way. The right-hand passage will lead to the foot of the aerie.