The Northern Pass is a location in Falskaar. It leads to a small cave with a barred gate: going near this gate will cause a dialogue box to appear on-screen, explaining that the gate is closed to prevent the harsh tundra area of the Northern Hold entering Falskaar. There are two chests with random loot and lots of mushrooms, but nothing more than this.
This location was originally intended to be part of some content relating to the Northern Hold, though these plans have since been abandoned after the release of 1.2.1