The Maintenance Station

The Maintenance Station was a depot for the Ytarran tram system underneath Urruk. It was a few weeks' march south of the Northern Terminus.
When the Maintenance Station was discovered by Vistrian archeologists, Delta sent a team of orcs to kill them and retrieve any Ytarran devices they found, presumably in a bid to keep the station hidden. They achieved this, also killing a team of orcs sent by Untor the Talker who had kidnapped the archeologists, although his reasons for doing so remain unclear.
Del attacked the Maintenance Station with an Ytarran digging machine as part of his plan to seize control of the Northern Terminus and eventually Polaron. The fact that his later assault on the Northern Terminus was from a different direction raises questions as to the exact nature of this plan.