 Altoona's location at the foot of the Allegheny front and its proximity to the Horseshoe Curve route over the mountains made the city a key location in the PRR's operations.By the 1920s, the Altoona railroad works employed 15,000 workers; by 1945 the PRR's facilities at Altoona had become the world's largest rail shop complex.In 2004, several members of the "Ghost Hunters" team investigated the Altoona Railroaders Memorial Museum, where the spirit of a railroad worker has reportedly been seen walking the halls.