To the OP, I am in Philly and used to park my bike in the Bellevue's parking garage--about a block from where you are (enter off of the alley by Applebees on 15th). Tons of people lock up on the lower levels, but I actually used to ride the elevator up to the 7th level and lock up near the car wash (as did a few others) because I was on my way to the gym at the top. I felt very secure up there and only stopped because I stopped going to that gym.