The National Library can house up to seven million items, using a compact shelving system. Its nine levels accommodate reading halls, closed stacks, a conference centre, research units and supporting facilities including a museum and exhibition space, nursery, restaurant and prayer hall. A key feature of the building is its use of natural light. Each of the four upper levels has been designed to introduce a maximum level of light into the reading halls - through clerestories - while avoiding direct sunlight. This has resulted in a stepped-pyramidal external appearance that responds to the irregular slope of the hilly site.