The 300 foot tall Atomium is a model of an iron molecule (Fe, baby!) built for the 1958 World Fair. This puppy is big enough that each ball can comfortably hold an exhibit about a) the World Fair b) the construction of the gigantic molecule or c) any number of extremely strange art exhibits including a floating flourescent cloud of stringy things and a suspended bunch of water molecule beds meant for children. Dude, Belgians are weird.