Every year, the first Monday of September in the United States is recognized as Labor Day. The national holiday dates back to 1894, when Congress declared the day a national holiday to honor the nation’s workforce and their contributions. Across the country, you can find evidence of early industrial and engineering wonders where workers toiled to help usher the nation into the modern era.

Established in the late 1880s, the Portland Cement Plant opened in San Antonio, Texas. It was the first plant of its kind west of the Mississippi to dig and process limestone for making cement. In Seattle, Washington, a gorgeous park stands in the shadows of an industrial giant. The massive factory-turned-park was once a gasification plant where coal and oil were tuned into synthetic gas. From industrial works that have been transformed into parks to all the abandoned kilns, furnaces, and mills that dot the U.S. landscape, here are 25 industrial wonders still standing in nostalgic glory.