King of Prussia to Downtown Philly

I'll be staying in King of Prussia this weekend and would like to spend a day in Philadelphia (Independence Hall, etc.) but rather than driving all the way into the city, is there a convenient parking lot and train/bus downtown?

I don't mind driving part way, and we do have a vehicle with us, I just thought using public transit could be better (and cheaper) than having a vehicle with us the whole time.

Any advice would be greatly appreciated!

Thank you!