The Horseshoe Curve is a three-track railroad curve operated in the modern day by the Norfolk Southern Railway’s Pittsburgh Line in Blair County, PA. Completed in 1854 by the Pennsylvania Railroad, the project was meant to lessen the slope of the Allegheny Mountains across Pennsylvania. The curve itself is about 2,375 feet long and 1,300 feet in diameter.

Not only an engineering success, the rail line has proved instrumental since its opening in transportation. After its opening, it replaced the time consuming Allegheny-Portage Railroad, the only other route across the mountains for large vehicles, transporting passengers and freight. In 1942, it was targeted during World War II by Nazi Germany due it unique position in transport.

The Horseshoe Curve has long been a tourist attraction, with its first observation park along the tracks opening in 1879. A renovated version of the park still exists and is operated by the Railroaders Memorial Museum in Altoona, PA.