Welcome to one of America's best bike trails, where you will discover a nearly level trail along winding rivers, shaded valleys, and traditional small towns.     The Great Allegheny Passage (GAP) rail-trail offers 135 miles of hiking and biking between Cumberland, MD, and Duquesne, PA, near Pittsburgh. In Cumberland, the GAP joins the C&O Canal Towpath, creating a continuous trail experience, 320 miles long, to Washington, DC.   The final few miles from Duquesne to Pittsburgh are still under construction. Check  Trail Status   for updates.    [GAP website]