When you look at the Atomium, you are looking at a science lesson turned into a building. Scientists know that iron - the same metal in a nail or a frying pan - is made of tiny units called atoms. The Atomium shows what one of those atoms would look like if you made it enormous.
The building was made for a big world fair in Brussels in 1958. Back then, scientists were very excited about atoms and what they could do. The architects wanted to celebrate science in the most eye-catching way possible, so they built an atom nine spheres tall.
Inside, there are exhibitions, a restaurant, and even a special room just for children. The tubes between the spheres contain escalators and lifts, so you travel up through the middle of the structure. From the top sphere, you can see all of Brussels spread out below.
The whole building is 102 metres tall - that is about the same height as a 34-storey block of flats. The shiny aluminium panels on the spheres were replaced in 2006 to make the building sparkle like new again. Today it is Belgium's most visited attraction.