This image presents the outer area of the Plum Brook Reactor facility.
In this historical photo from the U.S. space agency, the area just outside the containment vessel airlock (bottom right) is pictured in 1961. The reactor control room on the second floor is visible to the left.
The experiment control room is directly below it on the first level. On the second level to the right is a work area that was later segmented and enclosed for office space. In this picture, three of the "Reactor On" signs are illuminated, indicating that the reactor is in operation.
For more information browse the Plum Brook Facility Page.
Each weekday, SPACE.com looks back at the history of spaceflight through photos (archive).