Spatial justice, specifically accessibility, Universal Design and the fulfilment of human rights for vulnerable groups are increasingly deemed relevant issues in urban research and city-level agendas concerning public spaces. Although the development of older adult–friendly urban environments is part of the agenda to promote healthy ageing societies, public spaces (e.g., urban parks) often exclude those in the advanced age group in the community. This article offers a preliminary assessment of the older adult–friendly urban environments, hostile urban design elements and the everyday activities of older adults in urban parks by focusing on the extreme case of Sham Shui Po. This is a low-income, high-density and public space–scarce neighbourhood in Hong Kong, a city characterised by a rapidly ageing population and high socio-spatial inequality. Qualitative methods as environment audit, direct observations and video-recordings were used to investigate the physical environment and the older adults’ social and physical activities. Two representative urban parks are selected, the Nam Cheong Street Sitting-out Area (NCSA) and Tai Hang Tung Park (THTP). NCSA, located in a congested vehicular street median, allows independent mobility and is predominantly for intergenerational social activities. It is part of the daily route of residents and inhabitants from different ethnicities. Hostile design prevents the full use of seating facilities. THTP is a site for older adults to engage in physical activities and also accommodates large groups and caregivers. Defensive architecture and design layout may affect the group size in the parks, while sittable edges may directly contribute to the park use by older adults with physical disabilities, particularly near street crossings. The findings from this deprived neighbourhood highlight the critical role of landscape infrastructure for healthy ageing societies.