During the past few decades urbanization has been occurring at a very fast pace, claiming new territories by spatial expansion and occupying the last precious open spaces that are left. Urban growth, in combination with rapid climate change and the neglect of ecological processes, has had severe negative effects on the environment. Therefore, improving the quality of life in urban environments and transforming them into resilient cities has never been more relevant. At the same time, as current practices of urban development are failing to cope with the existing conditions, new opportunities are occurring. One of these opportunities are the unused and forgotten areas generated by urban growth that occupy large parts of the urban web. Despite their derelict appearance, these spaces provide a haven for spontaneous vegetation - the (so called) Third spaces. The Third space is a concept forged by the theories of Ignasi de Solà-Morales and Gilles Clément and refers to all types of places that constitute a territory of refuge for biological diversity. As a result of their abandonment, the Third spaces evolve into secondary landscapes that are colonized by pioneer species and perform ecological services. With Athens as the context of the proposal, this thesis aims to explore the potentialities of the Third spaces in the new processes of urbanization and re-envision their role as support for new ecological, morphological and cultural interrelations within the urban landscape. In order to do that, the area of Eleonas is chosen for intervention, as a characteristic example of an agglomeration of Third spaces among the post-industrial remnants and empty spaces found in the heart of Athens metropolitan area.