I think this is a promising early-ish draft of an underworld-epiphany poem. I like the mythologizing of the Underground (Heaney has a good but very different poem
on that), and the image of nothingness as the blackness in a tunnel. Lines 1-6 set things up economically and effectively. The scene is recognizable but is made strange through the weird sci-fi imagery of the steel maggot and the red eye. Weird or grotesque or scary metaphors are effective for defamiliarizing the familiar.
Lines 7-12, however, move into abstraction too soon and too extensively. The reflection there (“I thought of space . . . how I had found it squatting” etc.) feels sandwiched between the imagery of lines 1-6 and the concluding line rather than organically blending with them. So it comes across as sententious. This might be improved upon by getting rid of the “I thought of . . .” framework. I don’t think the reader needs to be told the narrator is having the thoughts. We’ve just been told the “I” saw the “world remade / as multiplying nothing,” so self-references to the N could be left out until the “my” near the end. That, and making lines 7-12 less “telly” could go a long way toward better capturing this Orpheus-like vision of the underworld.