Behind the majestic design and décor of Grand Central Terminal is a triumph of engineering and ingenuity. Grand Central didn’t just do things better than other train terminals. It did them differently. It pioneered new approaches to organizing space. It invented new technologies. And it overcame the daunting challenge of building a vast, durable, efficient train station—much of it buried deep underground—in the bustling center of the nation’s busiest city.

More and more people were riding more and more trains. Grand Central needed additional tracks…and efficient ways for passengers to reach those tracks. With little space to spread out, the station dug down. Engineers created a vast underground structure: four tracks in the Park Avenue tunnel and a 123-track train shed designed to support heavy locomotives plus the weight of the buildings overhead. A series of crossovers let trains reach any platform from any track. Inside the station, meanwhile, pedestrian ramps took passengers swiftly from level to level. The design also included a centralized hot water heating system—the largest of its kind at the time—with four miles of pipe serving the station and surrounding buildings.