In the past decades, we have witnessed a proliferation of interactive public displays for advertisement, entertainment and exhibition. We believe they also have great potential in the public spaces of caring environments if supported by related knowledge of design and research. This study explores how to design and evaluate interactive public displays in caring environments with a case study. In this paper, we describe the design process of OutLook, which is part of an initial participatory system specially designed for nursing homes to explore the possibilities of connecting people. It aims to enhance nursing home residents' social wellbeing through a "look-outside" and a "postcard-sending" metaphor. A field trial was performed to assess the effects of OutLook on nursing home residents' social behavior and feelings of connectedness. Key design factors for the effects and lessons learned were proposed as regard to design concept, design ideation, form of design, content, interfaces, interactions and field trial.