The Atomium's structure is that of an iron crystal, magnified 165 billion times, representing the technological advancements of the 1950s. An elevator (the world's fastest in 1958) takes visitors to the top sphere where there's a pretty nice view and a pretty expensive restaurant. The other spheres can be accessed through escalators in the tubes that connect the spheres.
The Atomium in Brussels is a rather large monument, though it doesn't seem to be very well known outside of Belgium. The monument was built for the World's Fair in Brussels in 1958 and is over 330 feet tall.