Whitetail Resort
has alpine skiing on 16 trails, just across the state line in nearby Mercersburg in southern Pennsylvania. (http://www.skiwhitetail.com/)You could drive from Hagerstown to Antietam National Battlefield, Fort Frederick State Park, or the C & O Canal.
Appalachian Trail
offers walking paths and breathtaking scenery from atop South Mountain.If you want more scenery you could cross the Potomac River into West Virginia or tour nearby smaller towns like Sharpsburg, Boonsboro, or Smithsburg.