## 1 Introduction  
More than half of the world's population currently resides in urban areas, and according to the United Nations, this number is projected to increase to two out of three people by 2050 [1]. Urbanization is a process affected by several constraints and issues concerning sustainability, emphasizing the need for nature-based solutions to prevail [2]. Prioritizing green solutions is crucial to increase the quality of life in cities through the improvement of sustainability. The presence and the awareness of abiotic and biotic parameters in urban and suburban areas is, in a broader vision, one of the most viable green solutions and serves as the initial step toward progress [3, 4]. The natural elements present in a city, which are declining in different aspects, are the geological characteristics of the settlement and the flora and fauna inhabiting green areas within cities [5, 6, 7]. The Investigation of the abiotic components of cities starts by considering that the establishment of an urban area is always influenced by geological factors [8, 9, 10]. Site selection for urban development derives from a well-defined set of variables. Among them, especially in ancient settlements, geological factors such as the topographic arrangement, the bedrock composition, and the water availability are all determining factors. The location is the primary parameter taken into account, as a favorable and strategic location can ensure efficient communication with other cities and increase trade and cultural exchanges. To achieve both of these conditions, morphological conditions (plain areas easily practicable) and hydrographic conditions (proximity to navigable rivers) play a key role. The topographic layout has a defensive function, minimizing also vulnerabilities to natural hazards such as landslides or floods. Underground resources such as lithotype outcropings at a settlement site are a crucial asset for obtaining building stones and can provide water supplies where aquifers are present. All these preliminary conditions are shared in a common geological component. For this reason, it is both easy and meaningful to promote and disseminate geological content to foster a different perspective and enhance awareness of urban areas. The geological and geomorphological conditions not only provide opportunities but also establish constraints on urban development, imposing boundaries between man-made and natural environments. This is particularly true in downtown areas with recent suburban development, where new technologies have allowed people to overcome the barriers imposed by natural conditions. In the past, the geological background in urban areas has been investigated and interpreted in relation to natural hazards and derived risk conditions such as flooding, landslides, or volcanic and seismic events [11; 12; 13; 14; 15; 16; 17]. Furthermore, in cases where urban development is constrained by morphological limits, natural green areas are preserved; these zones can be a precious resource for biodiversity preservation. The fauna and flora that populate our cities are surprising and largely not known, but they represent important and underestimated content. Actually, there is increasing attention to natural sciences as a tourist and educational resource within urban areas. The exploration of geoheriitage and the biotic component of cities has emerged as a promising and exciting field of investigation within the Earth sciences [9; 10; 18; 19; 20]. In addition, biotic presence is often undervalued because of the prevalent perception of the anthropic component and because historical and architectural values predominate in touristic themes, but this presence can be a meaningful component of the perception of urban spaces, if properly disclosed [21]. This article presents a case study focused on the promotion of naturalistic heritage within the urban area of Perugia, the capital town of the Umbria region (Central Italy).