I cleared out an entire ancient city

I have to start by saying I play in survival but peaceful mode. The kids yearn for the mines what can I say.

I cleared out an entire ancient city and made my own little city. I have my nether portal as the city center with storage underneath. I have a fully functioning train system that goes to various parts of the map. I have a campground with tents and cabins.

And I still have so much space to fill. What else should I do in this space? I consider myself a new builder so feedback is welcome.