Built in the middle of the 1800's, Horseshoe Curve on the Pennsylvania Railroad near Altoona, PA permitted rail travel between New York City and Chicago, giving Pennsylvania a major role in the development of the still young country. Virtually unchanged in design since it's initial construction, the curve is located at the end of a long "U" gradually sloping up two sides of a steep valley. Visitors gather and wait at the bend of the "U" to view the passing of long trains that still traverse this engineering marvel.