If you are into history/politics at all, you could check out the Constitution Center- it's way less boring than it sounds
. Good multimedia presentation involving a live actor, interactive exhibits, and "signer's hall" at the end which has life size bronze sculptures in realistic poses of the men that signed the constitution. One of my best friends and his girlfriend works there.
If you are into any sort of bar scene a nice area near by is "old city." (the area along Market closer to the river and a few blocks north and south). There is a type of place for everyone from the fancy (Steven Starr's Buddakan, Blu Martini, Tangerine) to the chill (Drinker's Tavern, Sugar Mom's, the Kyber). A terrific Cuban resturant with good mojitos and latin dancing after 10-11pm is Cuba Libre on 2nd street. You could also see if there are any concerts scheduled at Penn's landing.
Another fun area is South Street (basically 3rd through 7th on south) with a bunch more fun bars and hip stores. Good pizza can be found at Lorenzo's, which is notorious for it's anti-customer service
but in a funny way.
If you like art, the Philadelphia Art Museum is excellent and area is quite beautifull. You can do the tourist thing and run up the "Rocky" steps. Not far by are the Franklin Institute (very cool science museum with a giant IMAX movie screen) and the Museum of Natural History (great dinosaur skeletons). Also not so far from this area is the "Mutter" museum, which exhibits some of the strangest human medical anomalies preserved in fermaldehyde- just don't go if you're planning on eating right afterward
.
Just take some time to walk around- Philly is very approachable on foot and has lots of ethnic neighborhoods with good food, etc. There's also Chinatown (some cool martial arts stores there), the Redding Terminal Italian Market, etc. Hope this helps,
Jon
ps. The abbreviation is "Philly" not "Phili"
.