The Atomium in Brussels, Belgium was constructed for the 1958 World's Fair. The monument, built in the shape of a body-centered cubic iron crystal, was intended to honor the metals industry and celebrate the atomic age.
Each of the metal spheres is 18 meters in diameter; the entire structure stands 102 meters tall. The uppermost sphere houses a buffet restaurant and is accessible via escalators and an elevator in the central shaft. The aluminum-clad structure took 18 months to design and another 18 months to build.
More information available on the web at the atomium web site.