The Powerhouse is a historic building located on the campus of California Polytechnic State University in San Luis Obispo, California. Built from 1908 to 1910, the building was designed by William H. Weeks in the Mission Revival style. The Powerhouse was the last of the original buildings at Cal Poly to be constructed; however, it is now the only remaining original building on its campus. The building originally served as a power plant run by students and two full-time supervisors; it also held Mechanics and Electrical Engineering classes. The Powerhouse stopped generating power in the 1940s and was replaced entirely and abandoned in 1955. In 1967, the building found a new use when the school's College of Architecture and Environmental Design decided to hold classes there. The college continued to hold classes in the building even after the construction of a new architecture building, and only stopped in 1990 when the school's administration ordered the building to be abandoned.The Powerhouse was added to the National Register of Historic Places on July 30, 1993.