K-25 was a large facility built during World War II in Oak Ridge, Tennessee, as part of the Manhattan Project. Its primary purpose was to enrich uranium for the atomic bomb, using a process called gaseous diffusion. K-25 was one of the largest buildings in the world at the time, covering over 44 acres. The facility operated from 1945 until the late 1980s and played a crucial role in the development of nuclear energy. After its closure, K-25 was decommissioned and is now part of the Oak Ridge National Laboratory, which focuses on scientific research and development.