Turning sandbox into a fun game mode?

Hi all! I have a sandbox zoo I’ve been working on for a while now and am starting to fear that once I’m done building and have placed the animals it will all be… over?

I’m curious to hear how folks turn their sandbox builds into actual game modes either by adjusting settings or creating roleplay scenarios (breeding goals, conservation efforts, etc) in order to make the zoo playable in an interesting and challenging way.