I have lived in Pittsburgh since 2015. There is a lot to do outside of the Pirates game, although I would highly recommend going to a game just to see the stadium.
A couple things to do...You could easily walk from the PNC park to Heinz field and visit the Steelers Hall of Honor (see all the super bowl trophy's, players lockers, etc), there are some pretty cool bars around there to stop in and get a drink at. There are a few museaums you can check out on the N. Shore (Andy Warhol). You can walk the bridge over to Point State Park, and then right into downtown. I would go to Market Square and check out all the shops around that area, and I'd also highly recommend going to the Strip District while you are in town for lunch.
Lawrenceville or Shadyside have some great places to eat and drink at, they are both pretty fun for a night out.
You could actually take the ferry from the South Side to the North Shore and start your day that way, it's a really fun time. I definitely would avoid the South Side at night time though.