The concept of Zagreb's city hall was conceived as a complex of three volumes, but only one was built: the floating horizontal one made of stone, expecting a vertical counterpart on its western side, an administrative skyscraper. On its eastern side the auditorium and great conference hall can be found. Deep within the layout there is a covered atrium that acts as an airy entrance hall. An open atrium continues on it, with a green park flowing through the ground floor. The fresh, cool air from that atrium naturally airs and cools the upper rooms through installed vertical vents.