Also, as far as dayhikes, it's really not a difficult or a long drive to reach the Apalachian trail if you want to build a habit of hiking.

You just hop on 70 and drive to Myersville, MD. Or take 795 and keep going straight as it turns into 140 to 16 and hit Waynesboro, PA. In both cases it's really easy to pack the night before and not give much thought about directions because you just keep going straight and cruise, so you can just hop in the car in the morning and sleep drive to the trailhead.

That and Baltimore has three awesome Reservoirs nearby that have endless trail systems.