You could make that cylinder thing modular… I mean… make multiple versions of it like one that it opens like an airlock to the outside and that’s it. Another that it is an opening to a maze of tunnels for maintenance (either design the pieces for that or leave it to be added to anyone that would want to do that). Another option could be that it is a containment unit, it opens externally when unlocked and allows to put a human body or an alien body and such inside it.