Which part of this long title do I keep?

[liquidnonsense]

The name of my book on the current manuscript is G Corridor, or: Celia Cave and the School That No One Built. I've heard almost unanimously that this unusual title structure won't sell, and I get that—now the question is, which part do I keep? G Corridor (the working title of this novel since the beginning) or the more Harry-Potter-ish Celia Cave and the School That No One Built? And, wildcard—how about simply The School That No One Built?

Synopsis here if you're interested: https://querytracker.net/forum/index.php?topic=24015

[Tabris]

Celia Cave and the School No One Built sounds like a midgrade novel, and I would keep the entire title.  (Well, I'd remove "that" since it's unnecessary.)

If it's YA, I'd say "G Corridor in the Unbuilt School" or "Down the G Corridor"

If it's adult, "The School No One Built"

Keep in mind that there's a 50% chance the agent will change your title prior to submission, and another 75% chance the editorial board with change it again.

[liquidnonsense]

Celia Cave and the School No One Built sounds like a midgrade novel, and I would keep the entire title.  (Well, I'd remove "that" since it's unnecessary.)

If it's YA, I'd say "G Corridor in the Unbuilt School" or "Down the G Corridor"

If it's adult, "The School No One Built"

Keep in mind that there's a 50% chance the agent will change your title prior to submission, and another 75% chance the editorial board with change it again.

Interesting take! It's a YA novel, but I'm not quite sure I like either of those suggestions. "Unbuilt" suggests the school was never built at all, which isn't the case, it's more a commentary on the fact that nobody can figure out who built it and who's really running it and why. And "Down the G Corridor" strikes me as distinctly British (like "down the pub"—I can't picture an American student actually saying "down the G corridor") and also sounds to me more like a fun adventure than the dark mystery it is. But you make a good point at the end—ultimately this will probably be up to the publisher, so perhaps I'll let them decide!