The inauguration of the Metro de Medellín in 1995 represents the first major milestone in the process of social change that took place in Medellín, Colombia during the last three decades. The newly built public transport system drastically shortened travel times within the city and generated economic and social improvements for the entire population of Medellín. Despite this highly positive impact on the cities development, the construction of the Metro was accompanied by profound consequences on the existing urban fabric. The reinforced concrete viaduct, which leads the Metro line A via the Carrera Bolívar across the city‘s historic center radically transformed its urban surroundings. Medellíns once most representative road Carrera Bolívar today is characterized by underexposed, unclear and noise-affected public spaces and functions as hotspot for social and territorial conflicts between formality and informality. The following thesis addresses the historical development and the present situation of public spaces in the city center. An in-depth urban and socio-spatial analysis of the city-area crossed by the metro viaducts outlines the basis for an urban planning concept which is seeking for revaluation of the public spaces beneath and around the Metro viaduct. Through specific spatial interventions, the developed concept is implemented by four independently executable, but thematically related design projects, thus contributing to the newly developed, strong and sustainable identity of Medellíns city center.