Hi, apologies if this belongs in a master-thread.

This August I'll be in Philadelphia for a conference which ends on a Thursday, and I'm flying back to Spain Sunday night from JFK, so I have at most 72 hours in between.
Not been to Philadelphia or NYC before.
What would be the opportunity cost/next best alternative to spending Fri-Sun in NYC? Would like to visit DC but 2 days would not be enough.
I can't drive.
Thank you!