Light regulates our neurophysiology according to the natural day-night cycle and thus profoundly affects the livability of dense cities, in which we tend to live increasingly indoors and deeper underground. Circa Diem aims to raise awareness to the importance of our daily exposure to light for our health and well-being. Architecture and the urban fabric have the ability to control our access to natural light and do so by redirecting light rays through spatial form. By entering a cylindrical space, the visitor gets a sensorial experience of the passing of time through four phases of the 24-hour day—morning, midday, evening and night—thanks to a dynamic choreography of light and dark, color, words, and images alluding to the multiple dimensions of circadian rhythmicity in the built environment.