Virtua Fitness Center

Walk in through the main entrance and turn left, past the hair salon on your right, and just before you hit the front desk for the gym there's a little hallway on your right. The bathrooms are in that hallway. Just ask the gym front desk if you're not sure.

You can't really go past the gym desk if you're not a member, but the bathrooms are before the desk so anyone's good to use them. If you are looking for a gym, this one's on the pricier side but they do have a co-ed locker room with single stall lockable showers. They also offer a "free first day" you can discreetly use if you're in need of a place to shower, though you'll want to act like you're looking to use the gym itself.