IntroductionValues-based approaches are among the best practices for management and conservation planning. However, cultural significance assessments (of the attributes and values of cultural heritage) have generally been performed by experts (top-down) instead of including expert and nonexpert communities (top-down and bottom-up).ObjectivesThis paper presents a multitechnique approach in which different strategies are applied to assess the perceptions of cultural significance held by several actors (users, managers, staff, experts, children, students, virtual community) within the framework of the Keeping It Modern Grant awarded by the Getty Foundation (2020–2023) for the Ocean Swimming Pool (1960–1966) designed by Álvaro Siza in Matosinhos, Portugal.MethodInterviews, surveys, social media analysis, and workshops with children, students, and experts were adopted for the method, and, whenever possible, the ‘Imagine Ballarat’ Love, Change and Imagine questions were utilised as a resourceful instrument for assessing the significance attributed by multiple stakeholders.ResultsBased on the results, stakeholders’ opinions and values regarding the heritage site could be compared, which revealed the relationship between the values and the groups of actors, thereby deepening the complexity of heritage sites as National Monuments.ConclusionBy using this integrated perspective, we could define the cultural significance of a modern heritage site through an inclusive methodology while also establishing the grounds for conservation policies within a more broadly participative management of change.