The same way that the basements are 10 times bigger than the houses themselves.

The city used to be bigger perhaps. The sewer is older infrastructure from a forgotten age.

They really prioritize plumbing

I mean in a world that you can excavate a shit ton of dirt through magic why not make big ol’ poop tubes or basements?

Ten houses and a Taco Bell.

Please remember to tag your posts going forward. In the meantime, can you edit your post title to include [D4] please?