Superstructure walkway

Superstructure walkways were service corridors located between the individual floors of a Mondasian colony ship. (PROSE: Alit in Underland)

Layout and technology
Superstructure walkways were situated between the ground of the floor below them and the ceiling of the floor above, and were used for maintenance tasks, such as controlling the holograms projected onto the floor above. The walkways were comprised of numerous straight, burnished metal corridors and four-way junctions with smooth walls. The corridors were dully lit by strip-lights, and were short in height and width, barely allowing adult humanoids, such as and, to walk through them without hitting their heads on the ceiling. Monitoring stations and control panels were accessible from across the walkways.

The superstructure walkways accessed by the Master, Missy, Alit and Topknot, which were situated between Floor 0507 and Floor 0508, contained holo-emitters and auxiliary equipment, in addition to a service lift, which only travelled between the walkways underneath Floor 0507 and Floor 0508. This service lift was two metres in length and four metres in width, with a large deadlocked hatch. In addition, the lift featured thick metal strips, about a quarter of a metre in length, wrapped around it. (PROSE: Alit in Underland)

History
One night on Floor 0507 of the Mondasian colony ship, (PROSE: Alit in Underland) sometime after crashing on the floor in a shuttlecraft with the Twelfth Doctor, Bill Potts and Nardole, (TV: The Doctor Falls) and  accessed the superstructure walkways underneath Floor 0507 via the large hole made by the crashed shuttle when it burst through the solar farm's deck, as part of their discreet mission to reach Floor 0508 and regain control of the Cybermen. The pair used the rope ladder from the crashed shuttle to reach the walkways, but were unexpectedly joined by Alit, who had followed the Master and Missy from the solar farm's homestead and was being pursued by "Topknot", one of the patients originally sent to attack Floor 0507.

The trio journeyed through the superstructure walkways to find a service lift to Floor 0508, which Missy eventually located with her sonic umbrella. After the Master burned through the deadlock seals on the service lift's hatch with his laser screwdriver, Topknot, who had been slowly pursuing the trio, attacked, although Missy was able to distract it long enough for the Master to briefly disable it with his laser screwdriver, before altering Topknot's settings to recognise his vocal commands and stop registering lifeforms with two hearts as human. After Alit entered the service lift and deactivated its clamp, the Master, Missy and Topknot joined her, and Topknot activated the service lift's controls, sending the lift down into the skies of Floor 0508.

Later, on their return journey to Floor 0507, the Master, Missy and Alit bypassed the superstructure walkways by using an automated delivery system from the citadel on Floor 0508 to reach a produce store on Floor 0507. (PROSE: Alit in Underland)