Starting point of this thesis is the desire to explore the unfamiliar rooftops of the modern, Greek “polykatoikia” and the intention to integrate them into important structures of the vibrant city below. How would it be if the residents of a “polykatoikia” expressed their needs and desires in a common place, above it? And how could these common spaces organize a public square? We choose Eleftherias (Koumoundourou) Square, a central square of Athens, but also isolated and with heterogeneous population and we imagine it as a set of subspaces in two parallel levels: the ground level and the rooftops of the surrounding buildings. Aiming at enhancing multiculturalism, through acceptance of diversity activities, we design on rooftops the followings: a non-denominational chapel, art workshops for young people, a public library and leisure spaces. By preserving interesting privacy gradations, these features correlate (physically or mentally) with existing, inactive elements of the square: the Orthodox Church, the Municipal Gallery, the buried ancient traces of civilization and the dormant amphitheater. These fragments, pieces of a three-dimensional entity, form a new square that aspires to be a neighborhood core and an active part of Athens, suggesting finally, a way of thinking and acting for the modern city.