On Tuesday the Department of Energy and the National Park Service (NPS) signed the official memorandum of agreement to establish the Manhattan Project Historical Park. This does not mean that you can immediately visit the sites in the park (Hanford, Washington; Oak Ridge, Tennessee; and Los Alamos, New Mexico) and see lots of new signs and National Park Service-style displays and rangers and such. This agreement marks the end of the beginning for the park’s development.
The NPS estimates it will take two years to complete planning for the parks, and another three to five years to prepare the sites for public access. This planning and implementation will be done in cooperation with the Department of Energy, which still operates facilities at each of the sites.
This does not mean that you cannot visit these places. For the Hanford and Oak Ridge sites there are already means to tour some of the historical facilities. Walking tours of the town of Los Alamos are the best available option for the foreseeable future.
(The Bruggeman Agricultural Warehouse Complex at the Hanford site has, as far as I know, no direct connection to my family, even though I grew up within 30 miles of the place. Further research may prompt me to revise that statement, or at least clarify whether the same spelling is involved.)