In 1958 the Atomium was built for the Brussels Worlds Fair and never intended to be a permanent part of the Brussels landscape, but like the Eiffel tower for the French, once the fair was over the Belgians wanted to keep the giant structure.
Essentially the Atomium is a 335 foot tall giant iron crystal, replicated in shiny steel. It is formed by nine steel spheres arranged in the the shape that iron atoms take in their delta and alpha allotropes. (In irons gamma allotrope, there are extra atoms at the center of each face of the cube.) The Atomium is magnified 165 billion times the normal size of an iron crystal.
Designed by André Waterkeyn, (the director of a federation of metallurgical companies and not a sculptor by trade) one of the original ideas had been to build an upside down version of the Eiffel Tower, but in keeping with a 50s atomic age theme, they built the Atomium.
The Atomium was recently renovated and all but three of the steel spheres are available to enter and contain everything from an exhibition space, to a restaurant, to a place for Belgian school kids to have sleepovers.
Nearby the Atomium is Mini-Europe a Theme park featuring miniature replicas of European monuments