The article describes the project for the realization, through the system of the project financing, of a multi-level car park in a cavern in the hill of San Giusto, in the heart of the historic archaeological center of the city of Trieste. The idea of building a car park below the hill of San Giusto was born in 1996 with a first technical proposal to the Public Administration of Trieste. After a feasibility study, and following a formal proposal for the realization of the project with a Project Financing, dating back to 2002, brought to an end the planned tender procedure, in 2005 is given the Concession for the Design, Construction and Management of the park to the subject “Proponent” (today Park San Giusto Spa). The “Project”, since then, for geotechnical, environmental, urban and archaeological reasons, undergoes substantial changes until the version of the Final Design (2009) and then, in 2011, to the final of the Executive Project. The need to place the building below the hill of S. Giusto represent the only possible choice both for the urban set up of the area and for its central position. The construction of a such dimensions and characteristics park requires not inconsiderable economic resources, higher respect those referred for similar elevated and/or buried structures, but built in open-work, which could make the work impossible. With the system of the Project Financing together with a public financial contribution equal to 20.9% of the investment value of € 40.5 million, and a 36 years management of the park in the structure and in the street, it is possible to carry out the work for the benefit of citizenship with the positive social budget for the Grantor City. One aspect that has led to considerable close study examination is the research for a suitable ventilation system, proper to existing safety and fire standards, as the particular location of the park has made impossible the use of natural ventilation by means of shunt-type pipes, requiring a forced ventilation system. A fire engineering study, made to verify the equivalence of the two ventilation methods, shows that is possible to get air changes in case of standard use and in case of fire, by installing an adequate pipelines network, together with axial and centrifugal fans, to ensure an air capacity equal or greater than the natural foreseen by existing fire regulations. Other particularly “heavy” facets from the procedural point of view concerns the need to operate in urban city-centre areas, with architectural and archaeological restrictions, as well as the activities relative to the “expropriation” of deep property in a context characterized by private, public and state-owned subjects. All these aspects, as well as the authorization, law, technical and financial ones, has, as a matter of fact, led the whole project process up to 15 years after the initial detection by the municipality of Trieste of the need for a large container for parking in the center of the city of Trieste to the final approval of the Executive Project. Nevertheless, the possibility to realize in urban areas large underground volumes to be used as parking is an extremely functional solution to the chronic traffic and parking problems that plague big cities, resulting in opportunities to direct vehicular traffic along predefined conduits and free up more and more spaces to the pedestrian and cycling.