We stayed in Old City for a couple of nights. Independence Hall was worth a look, although the tour is super short. We also visited Benjamin Franklin Museum which is great for kids (lots of hands on exhibits). Worth sticking your nose in Christ Church where Franklin is buried. Quite enjoyed just...
We were back before all that smokiness rolled in fortunately. Philly was starting to get a little smoggy on the Friday. But we lucked out on weather and conditions. 25C in NYC and a hot 30-32C in Philadelphia. Pic from Top of the Rock.
Just returned from NYC and Philly at the weekend.
Been a couple of times previously and broadly agree with the advice given so far.
If you must go up the Empire State Building would definitely pre-book a ticket and consider whether buying the upgrade to skip the line might be a worthwhile...