My flight arrives in Philadelphia at 11:52 a.m. and my flight to Zurich doesn't leave until 7:15 p.m. that evening. This will be on a Sunday toward the end of June. Is this enough time to leave the airport? Is there anything close enough that would make it worth leaving?
The airport train to center city Philly runs hourly on Sundays, begins at Terminal F at 7 minutes past the hour. You likely won’t make the 12:07 so you are talking making center city at 1:35. You could wander some, the 3:55 from center city will get you to Terminal A at 4:17, or 4:55 at 5:17, for a 7:15 flight. No faster way in or out, especially if there is a baseball game at CBP. If you wanted you could get out earlier at Penn Med Station and wander around U of Penn.
OK Larry lives there so I defer to him. But, it’s a Sunday. Center city can be pretty dead and there are some shady sections. I think you’ll be getting off at 30th Street Station and I would not wander in that neighborhood. You could cab or Uber to the Philadelphia Museum of Art or enjoy a lunch at the Reading Terminal Market. Having said that I’ve done a lot of long layovers in my life but I have a rule I won’t violate-no leaving the airport when an international flight is involved. Just too much aggravation if it’s missed. While Philly is not the greatest airport for a long layover perhaps you can access a lounge.
If you enjoy U.S. History, I suggest an Uber to Old City. You could probably visit Independence Hall, Liberty Bell and maybe The Constitution Center before heading back to the airport. Some of these may have timed tickets, so be sure to check that out.
I agree with the suggestions from garyd. Taking UBER or LYFT on a Sunday would be the way to go. While Reading Terminal is a great place to go for food, several vendors (Amish and Mennonite) are not there on Sundays but you could still something to eat. The upside is it isn't generally as crowded on a Sunday, especially during the summer. If you are wanting a cheesesteak, you would do better going to Woodrow's Sandwich Shop which is a not far from Old City. I've never been impressed by the cheesesteaks at the Reading Terminal.
Be sure to allow ample time to return to the airport as traffic can be crazy due to sports events and people returning from the shore. Have a wonderful trip!