This large underground structure, revealed in Episodes 10 and 11 of Season Two, was presumably used to transfer cargo between vehicles or trains. A control room looks over the transfer aisle, where a crane is used to shift the cargo. A secondary tunnel, used for moving personnel and for maintenance needs, runs parallel to the tracks, and can be sealed off via hangar doors; these doors can be opened via a dual-control manual override.
At this point in the series, the facilities is suffering from poor maintenance, with many bits of the crane having fallen off and parts of the ceiling having collapsed onto the cargo below. The facility can only be reached via the maintenance tunnels and via the lower tunnel leading to BMESA #22.