This isn't really a sight-seeing thing, but grab a cheese steak! Pat's/Gino's are the famous spots where everyone takes photos, but IMO they're mostly tourist traps at this point. Worst cheese steaks I've had within 100 miles of Philly. Jim's is a good spot, plus it's on South Street which is a good area to walk around in.

The South Street area is also home to a bunch of mozaic murals by Isaiah Zagar, which are definitely worth checking out. There are official tours, but you can also just check out the neighborhood map here and explore some of them on your own: https://www.phillymagicgardens.org/about-us/mosaic-mural-map...

If you like walks, check out the Schuylkill River Trail - it got caught up in the recent flooding so I'm not sure what kind of shape it's in right now, but I assume it'll get cleaned up pretty quick if it hasn't been already. The view of 30th Street Station and a nearby USPS building is pretty cool at night. I've heard it can get a little sketchy if you're down on the trail at night, but as a 6ft tall white guy I never ran into any issues on the route walked home from work for ~8 months. Your mileage may vary, but the worst thing I ever encountered was kids my age smoking weed down by the river.