The spatial organization of post-socialist cities in Ukraine requires the creation of an adequate, comfortable urban environment in the conditions of crisis phenomena caused by problems of an economic, ecological, social and military nature. The problem of reforming cities requires a review of the "functionalism" paradigm and a new systemic consideration at three interconnected territorial levels: macro, meso, micro. The article describes the change in the paradigm of functionalism of spatial planning in post-Soviet countries, considers new methodologies of urban development of cities, proposes a new approach to the study of open public spaces, namely, as an element of the system of the urban planning environment. This approach reflects the important role of public spaces in shaping the urban fabric. Particular attention is paid to the integration processes of sustainable development of cities, which reveal a new meaning of human coexistence in the surrounding environment. In the context of a new look at open public space, the text describes the assumption "space creates the environment", which allows us to consider urban planning in a completely new dimension. The latest developments in scientific research on the typology of public spaces are separately considered. The article singles out physically accessible and physically inaccessible categories of public spaces. The article assumes that the city, as a cluster structure, is the sum of independent environments (elementary systems), which consist of public spaces united by certain characteristics. The issue of the micro-territorial level is considered, where the priority is the spatial organization of the city's public spaces on the basis of an urban cluster. An important feature is the pedestrian accessibility to various service functions of the urban environment. Based on the assumption, new approaches to the study of open public spaces at different urban planning levels are proposed, taking into account the human-oriented principles of the formation of a sustainable urban environment.