Well, you could take the R1 (train) to Suburban Station and use that as your launching point to:

-Reading Terminal Market , although you will be getting there quite close to closing time
-walk through City Hall
-Macy's department store (which is now just a shell of the once wonderful Wanamakers)
-maybe even Philly's Chinatown section

It will definitely be busy between 5-7 pm, although with only two hours you might be limited to just a couple on that (admittedly) sparse list.