I'm looking for a delicious sandwich in Old City Philadelphia
Paesano's is hardly a "few blocks" walk from even the northernmost border of Old City.
You're not going to find anything as interesting in Old City, but you can reliably get good sandwiches at Campo's and Gianfranco's.
South Street (what most people consider a few blocks walk from Old City) has the city's best gyro at South Street Souvlaki, and good middle eastern sandwiches at Alyan's
Old City get s bad rap. Yeah, it's a touristy destination but it does have some great stuff if you know where to look.
Eulogy- Napolean Burger (probably one of the top 3 burgers in the city)
Sassafras- Bison/Ostrich Burger w mixed green side salad
Cafe Ole- Excellent pressed panini's w a refreshing green iced tea.
Aromatic House of Kabob- Super Persian (sauteed spinach, tomato, mushroom, feta w either chicken or lamb) or Falafel sandwich.
Nick's- Roast Beef Italiano w au jus (awesome, cheap sandwich)
Campos- While they have the best cheesesteak in the neighborhood, have you tried the their grilled chicken sandwich (Valentines) or a Mamma Mia (Prosciutto, sopressatta, provi, roasted peppers) or the Caprese (mozz, tomato, prosciutto, peppers.......it's insane) Unfortuantely it is pricey and cash only.
Triumph- Hot Smoked Salmon Club
Race Street Cafe- I never had a bad anything at Race St. Excellent food including a nice lunch time selection of sandwiches.
Plus Mulberry Market and Sassafras Market make a great (cheap: $5-6) Boars Head hoagie and will load them up w all the fixings.