Part of the most contaminated nuclear site in the United States, long a tourist attraction, has just become a National Historic Landmark.

Between 1943 and 1963, the U.S. government built nine nuclear reactors near the Columbia River at a site named Hanford, in Washington state. Hanford’s B reactor supplied the plutonium for the bomb used on Nagasaki in World War II.

None of the reactors on the 560-square-mile site are operational today, but they still have a large influence on the area, which is in the middle of a huge cleanup effort. Underground tanks storing radioactive waste have leaked in the past, though none are leaking today. Spent nuclear fuel, which once lay in pools a few hundred feet from the Columbia River, is now in dry storage.

Despite the contamination, Hanford’s center role in the Manhattan Project has long been of interest to history buffs. Plus, the government restrictions surrounding the site have allowed wildlife to flourish in the absence of human interference. Near the new landmark, the Hanford Reach National Monument already draws about 60,000 visitors every year.

The National Park Service plans to open the B reactor to public tours. The other reactors are to be entombed with their cores. People visiting the area are not expected to be harmed by the contamination, but locals may be at a higher risk. The cleanup of Hanford will probably continue through the year 2030 and is expected to cost $50 billion.