Fs2004 scenery-tunkhannock viaduct, nicholson. Pa. A major vfr landmark, the viaduct was. Built by the lackawanna rr in 1915 and was. The largest concrete structure in the world. Until surpassed by the hoover dam. Still in. Use today, it remains one of the great. Feats of railroad engineering. Requires. Extreme landscapes by abacus or other terrain. Mesh enhancements for ne pennsylvania. Model. And textures by brien j. Miller.