The federal government created the Hanford nuclear reservation in 1943 as part of the Manhattan Project, and the Washington site is home to the world's first full-scale nuclear reactor. More than 20 years after Hanford stopped producing plutonium, it remains the country's most contaminated nuclear site. Cleanup is still under way. Visitors watch from a distance as workers in protective suits bury contaminated soil, and they tour the B Reactor, which features exhibits on the lives of the people who built it. The Department of Energy offers free tours of the Hanford site from April through September, but participants must reserve a seat in advance.