I love The City and The City and, while I am not finished it yet, it seems to me that the mystery remains a mystery - which is good!
I think I need to clarify. It was bothering me as I wrote my above post that I could not make my point more concise.
When it comes down to mystery and accomplishment, you can only have one or the other, not both. If a mysterious and unexplained force comes along and solves all the problems, that's cheating. The twin cities in The City and The City don't SOLVE problems, they pose mysteries.
To use the Gandalf example again, Gandalf solves very little of the problems of LOTR on-screen. When he solves problems, it's elsewhere. The reader is following certain characters, and Gandalf could have easily solved every problem they faced - but he wasn't always around. Gandalf left Helms Deep because had he not, he would have waved his hand and magically won the fight (the in-story justification for him leaving is good, but the meta-reason is probably this). The magic in LOTR is large-scale and incomprehensible to the little guys like Aragorn (yeah, even a long-lost King is a little guy!), and that makes it immensely interesting. But when that magic starts solving all the worlds problems it either a) loses the mystery, or b) feels like an asspull.
I hate hearing 'it's alternate history' as an excuse for poor writing. Yes, it is alternate history. This does not absolve you of the responsibility to explain and justify, it increases this responsibility. If you want something to be mysterious, fine. Just be careful with it; mystery becomes asspull when starts doing important things and solving plot points.
"When it comes down to mystery and accomplishment, you can only have one or the other, not both. If a mysterious and unexplained force comes along and solves all the problems, that's cheating. The twin cities in The City and The City don't SOLVE problems, they pose mysteries."
Ah, OK, when youput it like that, yes I agree.
I don't think its accurate, your point about tanks and stuff, yes the reality of the times prevented such things from being constructed, but the idea of how you could have tanks did exist.
Now, to suggest that a tank weighing 5000 pounds could be motorized by constructing it out of galvanic plates which harness telekinetic thought waves, might be an extremely outlandish notion, but the idea of a tank still existed.
If any of that makes any sense.
Maybe people forget that it is called "science FICTION" for a reason.
Not that I think you should have those kinds of unlikely inventions in your Steampunk story.