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.