DMs: What's a bit of world building on the micro-scale you're proud of?

[The Cats]

I have a setting (anthropomorphic animals of several species) where babies aren't born, rather cloned in laboratories controlled by the Church. Locals don't know about the laboratories, rather they are taught that is the city’s goddess (Bisbishna or Bishna for short) who directly blesses them with the gift of a newborn.

Nobody is given a baby unwillingly, rather families make a request to the church and is the goddess who decides if it’s appropriate to answer that request.

As babies are perceived as a favor from the goddess, there is practically no family that doesn’t wants to have one for their own, so is rare that the Church has problems assigning them. When it happens that there is a species with low population and no family is requesting for babies (for example Lions), then the Church clones them anyway and recruit them as monks, nuns, militia or whatever the city needs.

Sounds like a great hook for a horror/intrigue campaign.

Doomstalker's detailed explanation of how the twin-rivers affect the ecology and economy of the empire is the kind of stuff I love.