If you take a rental car into Philly there is an underground parking garage at the Constitution Center which is adjacent to Independence Hall and the Liberty Bell. All of the historic sites are in this same area and it is an easy walk around to the NPS sites. Check in advance about tours in Independence Hall as tickets are required and are handed out on the morning for same day tours with a specific tour time. It is not always easy to get a ticket if you arrive later in the morning and tickets are gone by 1 pm according to NPS. No tickets needed in January and February. No advanced tickets available.