First off, "northern Maryland" is a strange location description for a state that runs basically east-west and narrows to as little as a mile and a half in a north-south direction, so I'm going to assume that you are leaving from somewhere around Emmitsburg and have no interest in seeing things very close to 'home'. With that said, your basic route to Louisville would be to get on I-70 near Hagerstown and take that to Hancock, then use I-68 to Morgantown WV, I-79 south to Charleston, and I-64 west to Louisville. That would be a full day's drive at around 550 miles, depending on your actual starting point. Still there are a number of options for short stops that would allow you to get to Louisville in a day. Among them are Fort Frederick State Park (SP), Rocky Gap SP, Chesapeake and Ohio National Historic Park, the aforementioned Coopers Rock State Forest, Pricketts Fort SP, the Museum of American Glass, a Native American burial mound, Carter Caves SP, and horse farm tours.

Obviously, you couldn't visit all those, or spend a great deal of time at any of them, if you need to get to Louisville in a day. But if you have more time for your journey there is certainly no shortage of things to see and do en route.

AZBuck