PHL's public transit is strongest on an east-to-west basis. It has 3 major forms of public transit: bus (which goes every which way), subway (most useful for getting around downtown), and light rail (great for getting out of the city or comfortably to remote parts). You can buy a daypass (liberty pass) for about $10 at any major station (and a handful of the minor ones). Downtown, the most important stations are:
30th street station - a large, awesometastic building located on the river that divides the western "university" half of PHL and the eastern "downtown" half. Has rail, and if you head outside and down some stairs, has subway. Also has some shops for food.
Suburban station - a large underground station located beneath and around city hall. Attached to PHL's large underground concourses (you can walk a very long way without seeing daylight if you know what you're doing). Has rail and subway.
Market east - a large underground station located under a mall. Attached to PHL's large underground concourses, has rail and subway. The mall part closes at night; entering this after that requires you to know which of the million entrances are still open. East of suburban station.
Local food chains you should know about:
*Auntie Annie's - Excellent pretzels. A bit expensive
*Wawa - Excellent, really cheap subs made to order
Other places to go:
*Good Karma Cafe - Cozy coffeeshop near 30th street station (go east across the river and then a good ways south)
*Mugshots - Awesome coffeeshop much like the Beehive, and not terribly far from where a certain race will start. Head east from 30th street station across the river and then a good ways north. Right across from the Penn State Penitentiary (historical site, neat architecture, like a giant castle in the city).
*Chapterhouse - A lot like Té Café. Near market east, then head a ways south.
*There are plenty of restaurants I could suggest
*The Old City is the part of the city to the east of market east. Historical buildings, sites, narrow streets, neat shopping
*Downtown proper - near city hall, particularly southwest of there. Occupy is in front of city hall.
*University district - west of 30th street
*Chestnut hill - far north of the city, kind of snooty
*Main line - technically not in the city, and a ways northwest of 30th street station, a string of neighbourhoods linked by a light rail line (the R5-aka-Paoli-Malvern-Thorndale) to 30th street. This is where I live. Some parts are neat, a lot is dull.
*Squirrel Hill - Part of the University District, not good for much but making you wish you were in the other Squirrel Hill in PGH.
(there are more I've seen, but none of them are of particular interest)
It's a reasonably good city for walking and eating. There are Traitor Joes and Whole Foods all over the place.