Inside the cube

At the center of the library building in Stuttgart, is the so-called heart of the library, an exactly cube-shaped, empty space that extends over the lower four floors (basement and 1st to 3rd floors).
Above this, on the fourth to eighth floors, is the reading room with the open access area, in which galleries connected by stairs with bookshelves and reading places on the individual floors surround an atrium whose square base corresponds to that of the cube below and which expands upwards from floor to floor.