Where to travel in the US for a grad celebration

I'm graduating this month. My parents want to take me on a road trip somewhere in the US as a celebration. We're based in MD, so it would be great to spend <6 hours straight in the car. I'm not a beach person. I like walking in cities and taking photos of amazing views. I've already been to DC, NYC, Chicago, Savannah, and Orlando. My parents suggested Boston because they've been there. I've always wanted to go to Philly but that's a lot less of a big thing and I could do that another time. Any thoughts?