The Northern Terminus was a waystation on the Ytarran underground railway system, before the tunnel to Polaron. As Polaron was a secret military facility, those with insufficient clearance were told that this waystation was the northernmost point on the line, hence the name.
In the aftermath of the Ytarran extinction, the Northern Terminus was maintained by four Warforged named TR-4, CC-1, MN-8 and AB-21, along with the Worker Constructs under their command and a pair of giant Warforged who were presumably security. Over time, the Warforged began to break down due to lack of repair and MN-8 and CC-1 died of "old age". TR-4 and AB-21, however, were not content to go gentle into that good night and began to cannibalise parts from the other Warforged in order to prolong their own lives. After AB-21 died, TR-4 even managed to find a way to jury-rig incompatible parts, so that he could take from the giant Warforged. However, this greatly reduced his mobility and over time he began to go a little senile.
The Northern Terminus was equipped with a teleport delay field similar to the one in Polaron, which held anybody attempting to teleport into it for three rounds and indicated their size and destination using two beams of light which intersected in the area which will be filled by the teleporter when they arrive.