With the events of Sept. 11, 2001 in NYC and Washington, I thought it might be prudent to discuss the possibility of an attack. I seriously doubt that any of the tall buildings in Center City would be affected, mostly because we don't really house any giants of U.S. commerce.
Unfortunately, the area that is likely to be targetted is Olde City...that's the historic area. Within an 8 block area lies the Liberty Bell, Independence Hall, U.S. Mint, and many documents of historical significance. There are also many foreign embassies in the area.
In the event that anything should happen, head North. You'll be getting out of the way of emergency personnel and out of the general historic area faster that way.
Use big city survival tactics and stay in the tourist areas and you should be fine. Dress down when walking around (Don't look like a visitor). Use common sense, don't flash money, etc... Stay out of the many drug infested areas, it is very dangerous. I owned a store for three years in the Frankford section of North philly, I was lucky to get out alive!
As with any big city, practice discretion, but you don't need to be too paranoid here. Mainly, you just have to be a little more cautious at night.
The primary tourist areas, including Center City(Spring Garden to South, Delaware river to Schuylkill river), are fine in the daytime. At night, just be aware and stay where you see other people.
After 10PM, it's a good idea to stay off the subways (unless you're riding home from South Philly after a game); take a bus or taxi instead. Also, use caution at night at regional train stations (R trains) outside of Center City.
Other places tourists should generally avoid: North Philly, West Philly west of UPenn & Drexel areas.
AS IN MOST MAJOR CITIES,PHILLY HAS IT'S CRIME RATE.I SUGGEST THAT WHEN YOU VISIT PROTECT YOURSELF...DON'T CARRY LARGE SUMS OF MONEY AND FOR GOD'S SAKES, DON'T FLASH IT. THIS ATTRACTS THE WRONG ELEMENT TO YOU. DON'T WALK DOWN STREETS THAT ARE ISOLATED OR DESERTED...YOU NEVER KNOW WHO MIGHT BE LURKING IN THE SHADOWS. PHILLY, WELL DOWNTOWN PHILLY HAS MANY LITTLE PARKS. PERFECT FOR WALKING THROUGH FOR THOSE ROMANTIC MOMENTS UNDER THAT STAR LIT SKY...BUT IT'S ALSO A PERFECT PLACE TO GET AMBUSHED BY A MUGGER OR RAPIST...DON'T LOOSE YOUR COMMON SENSE, AS HISTORIC AS PHILLY LOOKS, IT'S STILL MODERN TIMES...ENJOY BUT USE CAUTION...PLEASE!!!!
While the city is apparently quite safe, always be careful when walking at night, especially if you're alone, and keep your valuable items with you, out of sight.