The R&D project Polariscope emerged from a collaboration between academia and a local historical archive. This initiative aims to create a digital platform that allows users to engage with cultural archives and events from various perspectives through collaborative storytelling assisted by Artificial Intelligence (AI) tools. The platform is designed as a digital community to gather contributions from both citizens and institutions to foster engaging digital experiences about meaningful cultural events and heritage archives that evoke collective memory. The paper presents the methodology and details of the User eXperience (UX) and User Interface (UI) design process iterated after the insights from focus groups with experts in archives, museology, cultural mediation, and community projects. The medium-fidelity prototype resulting from the gathered recommendations is under evaluation by users in a laboratory context. Afterwards, a new iteration and evaluation stage with field trials will occur during cultural events.