Probably the largest steam locomotive on tracks in the Western Hemisphere, this Nickel Plate monster was built in 1944 by the Lima Locomotive works for "fast freight service." This weekend it will make a special run from Hagerstown, Md., to Roanoke, Va. During its trip tomorrow through Shenandoah Valley, the train will stop for servicing and may be seen and photographed along Route 340 about 40 miles north of Waynesboro. This may be no magical mystery tour, but in an age of SSTs, ICBMs, MIRvs and all manner of largeness the Nickel Plate could be worth a look.