The Atomium is one of THE world's most unusual buildings you will ever see. It was actually built for the 1958 Exposition (The 1958 Brussels World's Fair). Shaped precisely like an atom, and designed by Andre Waterkeyn, the Atomium is 335-feet tall, with nine connected steel spheres. The total "building" forms the shape of an iron crystal magnified 165 billion times. The connecting "tubes" between the spheres (along the 12 edges of the cube and from all eight vertices to the centre)have escalators with exhibit halls and other public spaces. The one sphere provides a breathtaking view of the city. Not all the 18 m spheres of the Atomium are open for the public. The three upper ones do not have vertical supports and are not safe.
It's interesting how the Atomium got built. Originally the idea was to build an upside down version of the Eiffel Tower. The architect (Waterkeyn) figured an atomic structure was more suitable for the era. Interestingly enough, the idea was to only have this monument around for only 6 months. Obviously it was such a hit that it's still there. And, not only still there, but was renovated to replace the original external aluminium sheets with stainless steel. In a very smart fundraising move, the old aluminium was sold to the public for souvenirs. A triangular piece about 2 m long sold for €1,000. Renovations included redoing the exhibition spaces, adding a restaurant and a dormitory for kids called the Kids Sphere Hotel.