It depends on what you want to do and how far you want to drive. You don't really give an idea here.
Look at a map and figure out a driving range and a limit on how far you're willing to drive. Boston, NY, Philly, Richmond, Pittsburgh are all possible - and all of these places can be fun. If you want something more natural, go to the Poconos, the Appalachians, or the coast. All three of those are within a few hours and you can get a cute little place for you and your girlfriend.
I do road trips all the time and I always want a package of sports and music. I'll get on Pollstar and look for shows within driving range. Then I'll check schedules for every sports team within 3-10 hours of driving, depending on what I have in mind.
Good luck and have fun.