Reading Terminal Market in Philadelphia is one of the best places to sit for a few hours and sketch. There are so many booths there, selling everything from live plants to live lobster, and so many interesting people to draw. If you're ever in the area, I highly recommend trying a crepe from Profi's Creperie, some bizarre, but delicious molded chocolate from Chocolate by Mueller (when I was there, I saw chocolates shaped like teeth, noses, human hearts, and even rats!), and a pastry from the Flying Monkee Patisserie. Did I mention there are at least two produce markets, a beer garden and a live piano player for entertaining the crowds...Reading Terminal Market really is the best.