Thematic paths are a central aspect of urban policies for cultural heritage valorization. In fact, thematic paths are central spatial features for structuring the image of a historical landscape. Hence, this study proposes the cultural paths assessment tool (PAST) as a methodological framework for individuating a network of routes connecting cultural heritage components and for assessing their usefulness. Usefulness is herein defined as the potential of a street network to support the meaningful experience of a historical urban landscape. PAST combines space syntax techniques, a geographic information system, and a qualitative analysis within a multi-criteria analysis framework for addressing four aspects of connecting cultural heritage components, including: (i) the individuation of relevant assets; (ii) the identification of the sub-network of most central street segments; (iii) the definition of the street network of thematic routes; (iv) the assessment of the usefulness of thematic paths, according to the criteria of usability, imageability, and accessibility. The proposed methodology, applied to the historical district of Marina in the city of Cagliari in Italy, supports planning and design processes in two ways: (1) by identifying street segments and squares comprising a network of thematic routes; (2) by individuating high-leverage interventions for improving the usefulness of thematic routes. Consequently, the proposed study addresses the need to establish methodologies and analytic tools that support decision making processes for conserving, managing, and valorizing historic urban landscapes.