Designed by the engineer André Waterkeyn and architects André and Jean Polak, it stands tall. Its nine stainless steel clad spheres are connected in the shape of a unit cell that could represent an iron crystal magnified 165 billion times. Tubes connecting the spheres enclose stairs, escalators and an elevator (in the central, vertical tube) to allow access to the five habitable spheres, which contain exhibit halls and other public spaces. The top sphere includes a restaurant which has a panoramic view of Brussels. The building was completely renovated between 2004 and 2006 by the companies Jacques Delens and BESIX.